haskell-multiset: add version 0.2.2

The new version is currently unused, though, because it compiles only
with GHC 7.6.1 or later.

pkgs/development/libraries/haskell/multiset/0.2.2.nix

@@ -0,0 +1,13 @@
+{ cabal }:
+
+cabal.mkDerivation (self: {
+  pname = "multiset";
+  version = "0.2.2";
+  sha256 = "1g14c1zm4rdc8nxvb69k98h542wi24q2lpba1gpqjqspk4d0sjmn";
+  meta = {
+    description = "The Data.MultiSet container type";
+    license = self.stdenv.lib.licenses.bsd3;
+    platforms = self.ghc.meta.platforms;
+    maintainers = [ self.stdenv.lib.maintainers.andres ];
+  };
+})