Move the previously local import of threading to module level.
Move the previously local import of threading to module level.

This is cleaner and avoids lockups in obscure cases where a Queue
is instantiated while the import lock is already held by another thread.

OKed by Tim Peters.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator