[ Travis ] Removed unnecesary installation of cpphs
[ Travis ] Removed build with GHC 7.2.2

See issue https://code.google.com/p/agda/issues/detail?id=1340.
[ Travis ] Added 7.4.2 to the allow_failures section

See issue https://code.google.com/p/agda/issues/detail?id=1334.
[ Travis ] Fixed cabal-install path