Don't warn when installing externally hosted files

Users who opted to install externally hosted files were being warned
about the possiblility of the availability of those files would be
unreliable. However this has caused some contention and confusion
and at this point they've already decided to do it, so there's no
reason to tell them again.
Remove OSX from our build matrix

The Travis OSX builders are incredibly inconsistent for how long
they take to run our test suite. It is currently ranging anywhere
from ~15 minutes to well beyond 50 minutes, at which point it
times out.
Merge pull request #1807 from dstufft/remove-osx

Remove OSX from our build matrix
Remove the bundle functionality from pip