Allow calls to --version and similar.

Fixes cabal not being able to get the ghc version.
Add -package-db to to the parameters known to take an option.

Fixes command line parsing error on cabal build --with-ghc=ghc-parmake, so we can now use that with recent cabal + GHC 7.6.
Don't compile with -M if -c is already given
README: Add cabal instructions
Merge pull request #2 from nh2/fix-ghc-7.6

Fix ghc 7.6