Fix with 7.4 and 7.6 and make travis test them

This works for me.  I added the travis tests as a check.  GHC 7.6 comes with Cabal 1.16.  I'm not sure what 7.4 comes with, but since 1.10 seemed to work when I reported the 7.0 problem before I figured it would be a safe bet here.  The tests haven't finished running yet, but I thought I'd send this along anyway.