Adds a tweak for mock's output

I really really love voidspace's mock, but the output could use a little
love.  I have here a couple opt-in tweaks for the mock functions I use
the most.  I'd certainly be happy if mock included these, but I'm fine
with this.

To use, just import tweaksey from mocksey and call tweaksey.tweak_mock.
It'll monkey patch mock and also return it, so you don't need to import
mock and tweaksey.