7.7 dummy_threading -- Drop-in replacement for the threading module

# 7.7 `dummy_threading` -- Drop-in replacement for the `threading` module

This module provides a duplicate interface to the `threading` module. It is meant to be imported when the `thread` module is not provided on a platform.

Suggested usage is:

    try:
        import threading as _threading
    except ImportError:
        import dummy_threading as _threading

Be careful to not use this module where deadlock might occur from a thread being created that blocks waiting for another thread to be created. This often occurs with blocking I/O.