Restore travis to a working state.

The following pull requests restores travis to a state where globaleaks gets *tested* but **not** *installed* on a travis environment.

There have been tons of attempt, and tons of different commits adding/removing the same stuff. 
I tried to shrink them as much as possible, keeping them meaningful.
If you are willing to review only a smaller subset of commits, I will do my best to squash them to eventually reach an even smaller subset of commits.
The above implies that each developer *must* have both GLBackend and GLClient forks. 
Will be fixed once #996 gets done.