Major Haskell packages overhaul.

Several changes, some highlights:

  * Structure of haskell-packages.nix updated. It's now easier to
    select different default versions of packages for different
    versions of GHC.

  * GHC 7.0.2 is now default.

  * Haskell Platform 2011.2.0.0 has been added and is now default.

  * Several packages have been updated
    (gtk2hs, gitit, xmonad, darcs, ...).

  * Some old packages have been removed.

svn path=/nixpkgs/trunk/; revision=26288

pkgs/tools/misc/myhasktags/default.nix

@@ -1,4 +1,4 @@
-{fetchurl, stdenv, ghcReal} :
+{fetchurl, stdenv, ghcPlain} :
 
 /* use case:
 
@@ -29,7 +29,7 @@ stdenv.mkDerivation {
     ensureDir $out/bin
     ghc --make $src -o $out/bin/hasktags-modified
   '';
-  buildInputs = [ ghcReal ];
+  buildInputs = [ ghcPlain ];
 
   meta = {
     description = "my patched version of hasktags. Should be merged into hasktags?";