Add support for getting pkgDeps with Cabal <= 1.16
Fix ghc-7.8
Fall back to Cabal 1.16 format on runtime if extracting fails
Import HscTypes (HscEnv) with ghc <= 7.2
Merge pull request #248 from DanielG/dev-cabal-deps

Add support for getting pkgDeps with Cabal <= 1.16