Install brand new libgmp
Look in correct place for prebuilt libs
Expose ghc-includes to slug
Install prebuilt library to cache for its later restoration
Ghc 7.8 dist filename change
Install fancy libs before attempting to potentially build ghc
Docs and defaults for fresh versions
Merge pull request #53 from begriffs/ghc7.8

GHC 7.8, cabal-install 1.20.0.0