Wrap leave_module method in thread-safe manner

[jeremycarroll]

Running:
pylint --rcfile=dev-tools/pylint.rc -j 4 myapp
resulted in an overflow with:

    with_method(orig_method, *args, **kwargs)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 44, in ignore_import_warnings_for_related_fields
    return orig_method(self, node)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 316, in wrap_func
    with_method(orig_method, *args, **kwargs)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 44, in ignore_import_warnings_for_related_fields
    return orig_method(self, node)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 316, in wrap_func
    with_method(orig_method, *args, **kwargs)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 44, in ignore_import_warnings_for_related_fields
    return orig_method(self, node)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 316, in wrap_func

...

  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 316, in wrap_func
    with_method(orig_method, *args, **kwargs)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint_django/augmentations/__init__.py", line 44, in ignore_import_warnings_for_related_fields
    return orig_method(self, node)
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/pylint/checkers/variables.py", line 395, in leave_module
    if '__all__' in node.locals:
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/astroid/scoped_nodes.py", line 151, in locals
    util.attribute_to_function_warning('locals', 2.0, 'get_locals')
  File "/Users/jeremycarroll/work/syapse_apps/lib/python2.7/site-packages/astroid/util.py", line 27, in <lambda>
    return lambda *args: warnings.warn(message % args, warning, stacklevel=3)
RuntimeError: maximum recursion depth exceeded in __instancecheck__

I tracked this down to a race condition in the wrapping of the leave_module method, and this PR fixes that (there is still a race between different threads updating the method, but they no longer interfere with each other since the computation of the wrapped method is carefully guarded by the input to that computation being the original method)

[coveralls]

Coverage increased (+0.05%) to 87.692% when pulling cdc0b4d on jeremycarroll:master into ed19dff on landscapeio:master.

[coveralls]

Coverage increased (+0.05%) to 87.692% when pulling cdc0b4d on jeremycarroll:master into ed19dff on landscapeio:master.

[carlio]

Thank you this looks like it was a pain to track down!