[travis] Use ctest for building the project

Using ctest for everything has the advantage that the all the
individual steps (configure, build, test) will be submitted to the
dashboard, including all the warnings generated in all steps
[cdash] change project name to nix
[travis] Silence unused arguments warning for clang

Happens during linking, but we are not interested in it.
[travis] Use COMMIT instead of BRANCH for build name
[cdash] shorten commit id in build name to 7 chars

And remove "travis" from build name (that is clear from the site).
[cdash] attach travis configuration to the submission
[travis] enable irc notifications
Merge pull request #80 from gicmo/travis_ctest

[travis enhancements] Use ctest for building the project