Bug# 1011380 points out that locking operations such as
PyGILState_Ensure and PyGILState_Release should be
noop's if PyEval_InitThreads has not been called.

However, for reasons stated there, I dislike the
mechanism used in the patch supplied with the bug
report. The patch attached here uses a different mechanism:

 - within ceval.c, the PyEval_(Thread/Lock) functions
all use the existence of the GIL to check if
PyEval_InitThreads has been called. This matches
existing usage in ceval.c
 - a new API function PyEval_ThreadsInitialized() is
added to ceval.h that returns a true result only if the
GIL exists.
 - this new API is used by the PyGILState functions to
short-circuit their operation if the GIL does not exist.