First try at Travis-CI.
Download PyPy source before running tests.

Second try at Travis-CI.
Prevent PyPy's pytest from shadowing mine.

PyPy includes a vendorized version of pytest that is shadowing my newer
one because I have put that directory on the PYTHONPATH.
Add versions to test requirements.

This should ensure they get updated.
Only extract the necessary rpython directory.
Attempt to fix untar paths again.