[arch-haskell] Adding another data file for dependency "hints"

Hello, Since pacman's dependency specification is much less powerful than in Cabal, cabal2arch may output wrong version constraints while trying to approximate the true specified dependencies. I prefer this to dropping all version requirements when they cannot be expressed in the pacman's way. In order to get improved PKGBUILDs I thought we could have a better usage of the dependency resolution capabilities in the Cabal library, this is summed up in this commit http://github.com/remyoudompheng/archhaskell/commit/2e614b2 This adds an extra file, platform-provides.txt, that lists our preferred versions for various packages. For the moment I have filled it with the contents of Haskell Platform. Regards, -- Rémy.