Adds a dry-run for more info.
And more verbose info.
Show all installed packages.
Even more output, now from the travis file.
Try without apt.
More info on cabal.
Try a newer GHC to get things to work (hopefully).

The source for this .travis is https://github.com/ekmett/gl at commit
3a2435b982.
Remove old travis code.
Some whitespace cleanup.
Merge branch 'travis' into develop