Clean .travis.yml and adjust versions

This updates the travis.yml file.  As discussed earlier, it's adjusted to be (almost) entirely "include" commands instead of a confusing mix of includes, excludes, and implied builds.  It turns out Travis isn't happy if you only give includes, so I instead just had the default/implied builds be the "egg_info" command, and the tests are all run via includes.

It also makes the changes discussed in #784 by @astrofrog : the build for numpy 1.4.x is elimated, although because I'm adding in 1.7.x and some py 3.3 builds (which were previously missing), the number of builds is pretty much the same.

Note that this will completely replace #785 in content, but #785 should be merged first, because it should be backported to the 0.2.x branch to make the scipy tests run correctly there (@iguananaut), as 0.2.x should still support numpy 1.4.x .  Moving forward in astropy 0.3, we can drop numpy 1.4.x support, which this build reflects.