support SUSE packaging

many thanks to Jan Matějka for initiating this work
and providing patches for detecting OS, SPX license tags
and openSUSE Haskell packaging changes.

http://en.opensuse.org/openSUSE:Packaging_Haskell

https://github.com/yaccz/cabal-rpm/commit/3dd0639064a876d7ede17e504c5835866083c6d4
https://github.com/yaccz/cabal-rpm/commit/f9a7a50f678b9e4a0da7a8527b6c805a78c07b0b
https://github.com/yaccz/cabal-rpm/commit/b1837a25203f15414c5d83fb4cd9207cb5d966ce