Enhance Travis test to actually run ward

[fingolfin]

Right now, the travis tests only run build.sh, that's it.

It would be great if they could also actually use ward (resp. addguards2 etc.) on some actual code. Something simple should already help to prevent issues like #41

Of course a more comprehensive test could also clone the GAP repository and try to build its master branch...

Also, if we merge ward into the GAP repository, all of this comes essentially for free...

[ChrisJefferson]

I wrote a PR to do this (build GAP, run testinstall.sh), but I'm tempted to just move ward into the GAP repository instead -- it doesn't seem worth the pain of keeping externally, when it is used for nothing else.