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

[Rémy Oudompheng]

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.