Add Travis-CI integration, and minor improvements

[dannyedel]

While working on the Debian packaging of ball, I (or rather, my computer : ) spent quite a bit of time on building and executing the unittests repeatedly, while bisecting for patches.

While ball has CI servers, their build results and logs are not public, so I wrote up a travis-ci configuration file because it is so nicely integrated with GitHub - in the hope that it might be useful the next time around.

In the course of building current ball on the 14.04 'trusty' image I had to make some small changes in order to get a clean compile, or improve diagnostic output, these are on their own commits to ease reviewing.

It would be nice if this work could be merged back into the main repository.

Edit: Example log of a travis run: https://travis-ci.org/dannyedel/ball/builds/175482549

[tkemmer]

Thanks for your patches and suggestions! I'm not currently involved in the Travis part but I have merged your other commits as d1b6f27cd2e79e16662ddbe44c0277cf79927d94...b89f49f05595703ee66097e4ef6717b67659e052.