Simplify the use of wheels for Travis - #1355

@Cadair - it looks like this is going to work great! For now, I only see one wheel file missing: Numpy 1.5.1 on Python 2.7.

Yay, it works!

@Cadair - we won't merge this until you confirm that it's ok to use your wheelhouse (though we can merge before Numpy 1.5.1 is available since that's just one configuration)

@eteq - can you review this?

Deliberately restarting Travis to see if the Numpy 1.5.1 wheel works.

I am happy for you to merge this and use the wheelhouse. Let us know if you need more in the future.

Wow this is a lot easier than all the weird filename string manipulation I had to do (evidenced by the elimination of the very hacky .travis.pip.wheel. Is the magic taking care of that here all in the --use-wheels option to pip? I wonder if that would have just-worked if I'd done that for the old repo...

Anyway, there is one thing that's missing here, @astrofrog : it looks like -q is no longer included in any of the installs. Is that intended? The reason why it was in there before was that if builds had to fall back on doing the builds, sometimes they get very long, such that the Travis logs get unhappy and difficult to read (although maybe Travis has subsequently fixed that). You're probably not seeing that here because all of the wheels were actually obtained successfully, but if @Cadair's wheelhouse is down for some reason, the logs might suddenly become unreadable.

@eteq - good point, I'll add back the -q options - I had disabled for debugging.

Ahh, cool. In that case once they're in I think it looks good to go.

@eteq - I'll merge this now, and we can always update if we decide to have a mirror system (or other backup).