Update travis ci script to check all module stubs

[JukkaL]

Currently the travis.sh script only checks some package stubs, which is bad. It should look for all modules within packages under stubs/.

[o11c]

Handled in #721

[JukkaL]

The new location for stubs is typeshed/. We now check all Python 3 stubs, but we still don't check Python 2 stub files.

[gvanrossum]

Actually this is as fixed as it can be -- in ddf43e3 (in typeshed) I made several fixes to the runtests.py script. The only thing keeping us from perfection is that the sqlalchemy stubs are quite broken.

[gvanrossum]

To be clear, the typeshed's .travis.yml file now tests all stubs against mypy's master/HEAD, running mypy itself with Python 3.5, but passing --python-version flags values in [2.7, 3.2, 3.3, 3.4, 3.5].