Previously BPY_python_end wasn't called when scripts called sys.exit()
because BPY_python_end exited the Python interpreter.
Change this behavior to call BPY_python_end without exiting the Python
interpreter while freeing Blender/Python data.
While leaks in the context of sys.exit aren't especially important
it's generally preferable for sys.exit() to match Blender's code-paths
for exiting to avoid unexpected behavior.
e8df5cec83