added comment for IE9 Windows7 64bit bug

src/Global.js

@@ -37,6 +37,10 @@ Kinetic.Global = {
     //shapes hash.  rgb keys and shape values
     shapes: {},
     warn: function(str) {
+    	/*
+    	 * IE9 on Windows7 64bit will throw a JS error 
+    	 * if we don't use window.console in the conditional
+    	 */
         if(window.console && console.warn) {
             console.warn('Kinetic warning: ' + str);
         }