ghc-7.4 in the gentoo tree

A year has passed since last update from gentoo haskell team. Quite a few things have happened in haskell land since:

• ghc-7.2 and 7.4 were released by GHC HQ
• hackage got ever increasing ton of package bumps
• overlay got some of those updates
• cabal test suite by Thomas Tuegel became more popular
• and many others!