Interrupting with ctrl+c causes segfault after calling julia.Julia()

$ python --version
Python 3.7.0

$ julia --version
julia version 0.6.4

most recent pyjulia commit (from August 16): 25ab71cdc4fd17ef78127f3dd6e485d3efb8c327

I have to hit ctrl+c 4 times fast to cause the segfault.

The following is my Python REPL session.

```
Python 3.7.0 (default, Jun 28 2018, 13:15:42)
[GCC 7.2.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import julia
>>> julia.Julia()

```
[Here I hit ctrl+c 4 times fast]
```
>>> WARNING: Force throwing a SIGINT
fatal: error thrown and no exception handler available.
InterruptException()
unknown function (ip: 0x7f5f307905d2)
unknown function (ip: 0x7f5f2f658e42)
PyOS_Readline at python (unknown line)
unknown function (ip: 0x5629b3c2845b)
PyParser_ParseFileObject at python (unknown line)
PyParser_ASTFromFileObject at python (unknown line)
unknown function (ip: 0x5629b3cb318e)
PyRun_InteractiveLoopFlags at python (unknown line)
unknown function (ip: 0x5629b3cb348f)
unknown function (ip: 0x5629b3cb479f)
_Py_UnixMain at python (unknown line)
__libc_start_main at /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291
unknown function (ip: 0x5629b3da5e31)

signal (11): Segmentation fault
while loading no file, in expression starting on line 0
unknown function (ip: 0x5629b3ccd9bd)
unknown function (ip: 0x5629b3cb4e7a)
unknown function (ip: 0x5629b3da6382)
pydecref_ at ~/.julia/v0.6/PyCall/src/PyCall.jl:102 [inlined]
pydecref at ~/.julia/v0.6/PyCall/src/PyCall.jl:107
unknown function (ip: 0x7f5f088848f2)
jl_call_fptr_internal at /buildworker/worker/package_linux64/build/src/julia_internal.h:339 [inlined]
jl_call_method_internal at /buildworker/worker/package_linux64/build/src/julia_internal.h:358 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:1903
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1424 [inlined]
run_finalizer at /buildworker/worker/package_linux64/build/src/gc.c:111
jl_gc_run_finalizers_in_list at /buildworker/worker/package_linux64/build/src/gc.c:200
run_finalizers at /buildworker/worker/package_linux64/build/src/gc.c:234 [inlined]
jl_gc_run_all_finalizers at /buildworker/worker/package_linux64/build/src/gc.c:276
jl_atexit_hook at /buildworker/worker/package_linux64/build/src/init.c:265
jl_exit at /buildworker/worker/package_linux64/build/src/jl_uv.c:553
jl_no_exc_handler at /buildworker/worker/package_linux64/build/src/task.c:528
throw_internal at /buildworker/worker/package_linux64/build/src/task.c:553
jl_rethrow at /buildworker/worker/package_linux64/build/src/task.c:571
unknown function (ip: 0xffffffffffffffff)
Allocations: 3294270 (Pool: 3292993; Big: 1277); GC: 5
[1] 16996 segmentation fault (core dumped) python
```