Make mac+latex easier.

This makes two tweaks to Kirill's hard work:
* Add a base set of tex packages, so that we can use this for testing out of
the box.
* Change the way we handle paths, so that users don't have to source anything
in their `.travis.yml` unless they're doing something fancy (like installing
more of their own packages).
Merge branch 'kirill-merge'
Merge branch '52-latex' into wine

Conflicts:
	.travis.yml