Refcount / Garbage collection segfaulting issues

```
Continuation of: http://code.google.com/p/pyv8/source/detail?r=505

What steps will reproduce the problem?
1. raise an unhandled exception inside the testDestructor test

What is the expected output? What do you see instead?
A segfault

What version of the product are you using? On what operating system?
PyV8 revision 507, Python3.3, Linux

Please provide any additional information below.

It's curious that the test has changed from asserting a refcount of 3 to 4.
Inside the `testDestructor` you'll note that running `JSEngine.collect()`
immediately after `fn(obj)` will lower the refcount to only 3 , not back to 2.
I'm not sure what this means?

Here's the gdb backtrace.

(gdb) run build/lib.linux-x86_64-3.3/PyV8.py
Starting program: /usr/bin/python3.3 build/lib.linux-x86_64-3.3/PyV8.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff7ff1700 (LWP 9488)]
......................[New Thread 0x7ffff49ab700 (LWP 9489)]
[New Thread 0x7fffeffff700 (LWP 9490)]
[Thread 0x7fffeffff700 (LWP 9490) exited]
[Thread 0x7ffff49ab700 (LWP 9489) exited]
.[New Thread 0x7ffff49ab700 (LWP 9491)]
.......4
F...................[Thread 0x7ffff49ab700 (LWP 9491) exited]

Program received signal SIGSEGV, Segmentation fault.
0x000000000042f976 in ?? ()
(gdb) bt
#0 0x000000000042f976 in ?? ()
#1 0x00007ffff51dc337 in ~object_base (this=,
__in_chrg=)
at /home/nick/py3/boost_1_53_0/boost/python/object_core.hpp:526
#2 ~object (this=0xb7c840, __in_chrg=) at
/home/nick/py3/boost_1_53_0/boost/python/object_core.hpp:318
#3 ~object (this=0xb7c840, __in_chrg=) at src/Wrapper.cpp:1732
#4 ~auto_ptr (this=, __in_chrg=) at
/usr/include/c++/4.6/backward/auto_ptr.h:170
#5 ObjectTracer::~ObjectTracer (this=, __in_chrg=) at src/Wrapper.cpp:1732
#6 0x00007ffff51dc401 in ~auto_ptr (this=,
__in_chrg=) at /usr/include/c++/4.6/backward/auto_ptr.h:170
#7 ContextTracer::~ContextTracer (this=0xc9ce60, __in_chrg=) at
src/Wrapper.cpp:1833
#8 0x00007ffff51dc491 in ContextTracer::WeakCallback (value=...,
parameter=0xc9ce60) at src/Wrapper.cpp:1838
#9 0x00007ffff52b8408 in
v8::internal::GlobalHandles::PostGarbageCollectionProcessing(v8::internal::Garba
geCollector, v8::internal::GCTracer*) () from
/home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#10 0x00007ffff52d5693 in
v8::internal::Heap::PerformGarbageCollection(v8::internal::GarbageCollector,
v8::internal::GCTracer*) ()
from /home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#11 0x00007ffff52d6f6e in
v8::internal::Heap::CollectGarbage(v8::internal::AllocationSpace,
v8::internal::GarbageCollector, char const*, char const*) () from
/home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#12 0x00007ffff538dc3f in
v8::internal::JSObject::UpdateMapCodeCache(v8::internal::Handle, v8::internal::Handle,
v8::internal::Handle) ()
from /home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#13 0x00007ffff543087d in
v8::internal::StubCache::ComputeLoadGlobal(v8::internal::Handle, v8::internal::Handle,
v8::internal::Handle,
v8::internal::Handle, bool) ()
from /home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#14 0x00007ffff530f70a in
v8::internal::LoadIC::ComputeLoadMonomorphic(v8::internal::LookupResult*,
v8::internal::Handle,
v8::internal::Handle) () from
/home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#15 0x00007ffff531280d in
v8::internal::LoadIC::UpdateCaches(v8::internal::LookupResult*,
v8::internal::InlineCacheState, v8::internal::Handle,
v8::internal::Handle) ()
from /home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
---Type to continue, or q to quit---
#16 0x00007ffff5313124 in
v8::internal::LoadIC::Load(v8::internal::InlineCacheState,
v8::internal::Handle,
v8::internal::Handle) () from
/home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#17 0x00007ffff5313381 in v8::internal::LoadIC_Miss(v8::internal::Arguments,
v8::internal::Isolate*) ()
from /home/nick/py3/pyv8/build/lib.linux-x86_64-3.3/_PyV8.cpython-33m.so
#18 0x00003852b78062ee in ?? ()
#19 0x00003852b7806241 in ?? ()
#20 0x00007fffffffb9f0 in ?? ()
#21 0x00007fffffffba38 in ?? ()
#22 0x00003852b78837e6 in ?? ()
#23 0x00002e95e7209a71 in ?? ()
#24 0x000005a8a53929f1 in ?? ()
#25 0x000032b4656081d1 in ?? ()
#26 0x000032b4656081d1 in ?? ()
#27 0x000005a8a537b2d9 in ?? ()
#28 0x00007fffffffba78 in ?? ()
#29 0x00003852b7825b04 in ?? ()
#30 0x000032b4656082a1 in ?? ()
#31 0x000005a8a5392b11 in ?? ()
#32 0x000032b4656081d1 in ?? ()
#33 0x00003852b7825a41 in ?? ()
#34 0x0000000800000000 in ?? ()
#35 0x0000000000000000 in ?? ()
(gdb)

```

Original issue reported on code.google.com by `ndudfi...@gmail.com` on 8 Feb 2013 at 5:57