titaniumsdk: Added version 3.1 next to version 2.1, and make it configurable

pkgs/development/mobile/titaniumenv/default.nix

@@ -1,11 +1,19 @@
-{pkgs, pkgs_i686}:
+{pkgs, pkgs_i686, version ? "3.1"}:
 
+let
+  titaniumexpr = if version == "2.1" then
+    ./titaniumsdk-2.1.nix
+  else if version == "3.1" then
+    ./titaniumsdk.nix
+  else
+    throw "Unknown Titanium SDK version: ${version}";
+in
 rec {
   androidenv = pkgs.androidenv;
 
   xcodeenv = if pkgs.stdenv.system == "x86_64-darwin" then pkgs.xcodeenv else null;
-
-  titaniumsdk = import ./titaniumsdk.nix {
+  
+  titaniumsdk = import titaniumexpr {
     inherit (pkgs) stdenv fetchurl unzip makeWrapper python jdk;
   };