[Python-Dev] dummy_thread (#622537), part 2

[Brett Cannon]

Wrote ``dummy_threading``.  Thanks to the recent importing discussion and
one of Martin's replies to my previous announcement for this patch I
figured out how to do it while still using ``threading``.
``sys.modules`` is your friend (as long as you treat it nicely).

So the patch is ready for review again.  Tim mentioned he was going to
have a look, but I will let him say whether he is going to still look at
it now.

All relevent info is in the patch.

-Brett