Add PIXI to the Phaser namespace

Hackish solution to make it possible to access PIXI directly from a game.

Author: mkristo

src/Phaser.js

@@ -114,6 +114,7 @@ var Phaser = Phaser || {
         DEFAULT:0,
         LINEAR:0,
         NEAREST:1
-    }
+    },
 
+    PIXI: PIXI || {}
 };