cabal.mkDerivation: Use defaultMain if no Setup.{l,}hs exists.

This mirrors the default behaviour of cabal-install for the Simple build type
coq_HEAD: 8.5pre-fff9e2f7 -> 8.5pre-8bc01590
texlive: Fix build for users of Mavericks
haskell-aeson: Add version 0.7.0.6