7.6 dummy_thread -- Drop-in replacement for the thread module

# 7.6 `dummy_thread` -- Drop-in replacement for the `thread` module

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

Suggested usage is:

    try:
        import thread as _thread
    except ImportError:
        import dummy_thread as _thread

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.