Remove all references to Data.Version.versionTags

Data.Version.versionTags will be deprecated in GHC 7.10, see https://ghc.haskell.org/trac/ghc/ticket/2496.

I have a patch ready for GHC, but to let GHC validate without warnings I would need Cabal to not refer to versionTags in files created during the build, 'autogen/*_hsc2hs.hs', (via the functions build ->  initialBuildSteps -> writeAutogenFiles in Cabal/Distribution/Simple/Build.hs). Currently it does so by calling show on a Version in Cabal/Distribution/Simple/Build/PathsModule.hs.

Extra: this patch removes all references to versionTags, to let Cabal itself compile without extra deprecation warnings once 7.10 comes out.