Moved the cabal build driver function from development/libraries/haskell/cabal to build-support/cabal.

This change also resolves the "cabal" vs. "Cabal" ambiguity on file systems
that don't distinguish case.

svn path=/nixpkgs/trunk/; revision=32401

pkgs/top-level/haskell-packages.nix

@@ -121,7 +121,7 @@ let result = let callPackage = x : y : modifyPrio (newScope result.final x y);
   # This is the Cabal builder, the function we use to build most Haskell
   # packages. It isn't the Cabal library, which is spelled "Cabal".
 
-  cabal = callPackage ../development/libraries/haskell/cabal/cabal.nix {
+  cabal = callPackage ../build-support/cabal {
     enableLibraryProfiling = enableLibraryProfiling;
   };