Segfault while indexing libtorrent

Some info from the debugger:

```
(gdb) bt
#0 __strcmp_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcmp-sse2-unaligned.S:29
#1 0x00007f1a806f9d7b in ?? () from /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0
#2 0x00007f1a806fa39d in boost::python::converter::registry::insert(void* (*)(_object*), void (*)(_object*, boost::python::converter::rvalue_from_python_stage1_data*), boost::python::type_info, _typeobject const* (*)()) () from /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0
#3 0x00007f1a8070daf1 in boost::python::converter::initialize_builtin_converters() () from /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0
#4 0x00007f1a806f9e14 in ?? () from /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0
#5 0x00007f1a806ee2b4 in ?? () from /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0
#6 0x0000003ae140f2da in call_init (l=, argc=argc@entry=5, argv=argv@entry=0x7ffc8f270258, env=env@entry=0x7f1ab029b470) at dl-init.c:72
#7 0x0000003ae140f3eb in call_init (env=0x7f1ab029b470, argv=0x7ffc8f270258, argc=5, l=) at dl-init.c:30
#8 _dl_init (main_map=main_map@entry=0x7f1ab323c500, argc=5, argv=0x7ffc8f270258, env=0x7f1ab029b470) at dl-init.c:120
#9 0x0000003ae14138d0 in dl_open_worker (a=a@entry=0x7f1ab78c2818) at dl-open.c:575
#10 0x0000003ae140f184 in _dl_catch_error (objname=objname@entry=0x7f1ab78c2808, errstring=errstring@entry=0x7f1ab78c2810, mallocedp=mallocedp@entry=0x7f1ab78c2807, operate=operate@entry=0x3ae1413500 , args=args@entry=0x7f1ab78c2818) at dl-error.c:187
#11 0x0000003ae1413081 in _dl_open (file=0x7f1ab3249100 "/usr/lib/python2.7/dist-packages/libtorrent.so", mode=-2147483646, caller_dlopen=0x522fd3 <_PyImport_GetDynLoadFunc+243>, nsid=-2, argc=5, argv=, env=0x7f1ab029b470) at dl-open.c:660
#12 0x0000003ae1c00f09 in dlopen_doit (a=a@entry=0x7f1ab78c2a30) at dlopen.c:66
#13 0x0000003ae140f184 in _dl_catch_error (objname=0x7f1ab01d8d00, errstring=0x7f1ab01d8d08, mallocedp=0x7f1ab01d8cf8, operate=0x3ae1c00eb0 , args=0x7f1ab78c2a30) at dl-error.c:187
#14 0x0000003ae1c01521 in _dlerror_run (operate=operate@entry=0x3ae1c00eb0 , args=args@entry=0x7f1ab78c2a30) at dlerror.c:163
#15 0x0000003ae1c00fa1 in __dlopen (file=, mode=) at dlopen.c:87
#16 0x0000000000522fd3 in _PyImport_GetDynLoadFunc () at ../Python/dynload_shlib.c:140
#17 0x0000000000522baf in _PyImport_LoadDynamicModule () at ../Python/importdl.c:42
#18 0x00000000004af535 in import_submodule.lto_priv.1579 (fullname=0x7f1ab2cc6d20 "libtorrent", subname=0x7f1ab2cc6d20 "libtorrent", mod=) at ../Python/import.c:2722
#19 load_next (p_buflen=, buf=0x7f1ab2cc6d20 "libtorrent", p_name=, altmod=, mod=) at ../Python/import.c:2537
#20 import_module_level.isra.3 (level=, fromlist=['.'], globals=, name=) at ../Python/import.c:2246
#21 PyImport_ImportModuleLevel () at ../Python/import.c:2310
#22 0x00000000004b1408 in builtin___import__ () at ../Python/bltinmodule.c:49
#23 0x00000000004cb0a5 in do_call (nk=, na=1, pp_stack=0x7f1ab78c2f30, func=) at ../Python/ceval.c:4564
#24 call_function (oparg=, pp_stack=0x7f1ab78c2f30) at ../Python/ceval.c:4372
#25 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#26 0x00000000004c2bd5 in PyEval_EvalCodeEx () at ../Python/ceval.c:3582
#27 0x00000000004cacac in fast_function (nk=1, na=, n=, pp_stack=0x7f1ab78c3140, func=) at ../Python/ceval.c:4445
#28 call_function (oparg=, pp_stack=0x7f1ab78c3140) at ../Python/ceval.c:4370
#29 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#30 0x00000000004ca1af in fast_function (nk=, na=, n=, pp_stack=0x7f1ab78c3290, func=) at ../Python/ceval.c:4435
#31 call_function (oparg=, pp_stack=0x7f1ab78c3290) at ../Python/ceval.c:4370
#32 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#33 0x00000000004ca1af in fast_function (nk=, na=, n=, pp_stack=0x7f1ab78c33e0, func=) at ../Python/ceval.c:4435
#34 call_function (oparg=, pp_stack=0x7f1ab78c33e0) at ../Python/ceval.c:4370
#35 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#36 0x00000000004ca1af in fast_function (nk=, na=, n=, pp_stack=0x7f1ab78c3530, func=) at ../Python/ceval.c:4435
#37 call_function (oparg=, pp_stack=0x7f1ab78c3530) at ../Python/ceval.c:4370
#38 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#39 0x00000000004c2bd5 in PyEval_EvalCodeEx () at ../Python/ceval.c:3582
#40 0x00000000004def28 in function_call.lto_priv () at ../Objects/funcobject.c:523
#41 0x00000000004b1143 in PyObject_Call () at ../Objects/abstract.c:2546
#42 0x00000000004c715f in ext_do_call (nk=, na=, flags=, pp_stack=0x7f1ab78c37e8, func=) at ../Python/ceval.c:4664
#43 PyEval_EvalFrameEx () at ../Python/ceval.c:3026
#44 0x00000000004ca1af in fast_function (nk=, na=, n=, pp_stack=0x7f1ab78c3930, func=) at ../Python/ceval.c:4435
#45 call_function (oparg=, pp_stack=0x7f1ab78c3930) at ../Python/ceval.c:4370
#46 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#47 0x00000000004ca1af in fast_function (nk=, na=, n=, pp_stack=0x7f1ab78c3a80, func=) at ../Python/ceval.c:4435
#48 call_function (oparg=, pp_stack=0x7f1ab78c3a80) at ../Python/ceval.c:4370
#49 PyEval_EvalFrameEx () at ../Python/ceval.c:2987
#50 0x00000000004c2bd5 in PyEval_EvalCodeEx () at ../Python/ceval.c:3582
#51 0x00000000004ded6e in function_call.lto_priv () at ../Objects/funcobject.c:523
#52 0x00000000004b1143 in PyObject_Call () at ../Objects/abstract.c:2546
#53 0x00000000004f4d7e in instancemethod_call.lto_priv () at ../Objects/classobject.c:2602
#54 0x00000000004b1143 in PyObject_Call () at ../Objects/abstract.c:2546
#55 0x00000000004ce9e0 in PyEval_CallObjectWithKeywords () at ../Python/ceval.c:4219
#56 0x0000000000595722 in t_bootstrap () at ../Modules/threadmodule.c:620
#57 0x0000003ae2007454 in start_thread (arg=0x7f1ab78c4700) at pthread_create.c:334
#58 0x0000003ae18e8eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
```

```
(gdb) py-bt
Traceback (most recent call first):
File "/home/whirm/.local/lib/python2.7/site-packages/importmagic/index.py", line 188, in index_builtin
module = __import__(name, fromlist=['.'])
File "/home/whirm/.local/lib/python2.7/site-packages/importmagic/index.py", line 180, in _index_module
self.index_builtin(import_path, location=location)
File "/home/whirm/.local/lib/python2.7/site-packages/importmagic/index.py", line 159, in index_path
self._index_module(root, location)
File "/home/whirm/.local/lib/python2.7/site-packages/importmagic/index.py", line 207, in build_index
self.index_path(filename)
File "/home/whirm/.emacs.d/var/el-get/elpy/elpy/impmagic.py", line 44, in _build_symbol_index
index.build_index([project_root] + sys.path)
File "/usr/lib/python2.7/threading.py", line 754, in run
self.__target(*self.__args, **self.__kwargs)
File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
self.run()
File "/usr/lib/python2.7/threading.py", line 774, in __bootstrap
self.__bootstrap_inner()
```

```
(gdb) py-print name
local 'name' = 'libtorrent'
```

```
(gdb) py-locals
self = , score=, location='L', _tree={'filecmp': , 'dircmp': , 'cmp': }, _lib_locations=None, _name='filecmp', _parent=<...>, _blacklist_re=<_sre.SRE_Pattern at remote 0x7f1ab8542030>, score=, location='S', _tree={'dircmp': , 'cmpfiles': , 'cmp': }) at remote 0x7f1ab6b17650>, 'Canvas': , _blacklist_re=<_sre.SRE_Pattern at remote 0x7f1ab8542030>, score=, location='S', _tree={'Canvas': 188 module = __import__(name, fromlist=['.'])
189 except Exception:
190 logger.debug('failed to index builtin module %s', name)
191 return
192
193 with self.enter(basename, location=location) as subtree:
(gdb)
```

Note that running `module = __import__('libtorrent', fromlist=['.'])` from ipython works just fine.

(I originally created the issue at https://github.com/jorgenschaefer/elpy/issues/834)

Let me know if you need any more info.

If you don't think that can be fixed on the importmagic side, would you accept a PR that adds a module blacklisting feature?

Thanks!