Tests pass on both Python 2 and 3 now. Yay!
MockFont is handy for mtiLib.__init__:main(). Not sure how useful it is
otherwise, and what to replace it with.
I'll first make Python 2 and 3 both generate same output for tests with
MockFont, then will probably hardcode glyphorder and remove MockFont
completely and remove hacks I added to make tests work with MockFont.
