Make .cabal meta-data more accurate

Authored by hvr on Jan 24 2016, 3:07 AM.

Description

Make .cabal meta-data more accurate

We need this so cabal (this is even more important with the upcoming
nix-style cabal features) can do a proper job so this is a pre-requisite
for the new build-system being used by default for GHC anyway, as we
need to be as accurate as possible with the build specification to give
git bisect a chance of remaining usable.