Store last mouse position in a variable instead of document datastore

It's hundred times faster. See http://jsperf.com/data-vs-variable

Author: byroot

select2.js

@@ -40,7 +40,7 @@
         return;
     }
 
-    var KEY, AbstractSelect2, SingleSelect2, MultiSelect2, nextUid, sizer;
+    var KEY, AbstractSelect2, SingleSelect2, MultiSelect2, nextUid, sizer, lastMousePosition;
 
     KEY = {
         TAB: 9,
@@ -163,7 +163,7 @@
     }
 
     $(document).delegate("body", "mousemove", function (e) {
-        $.data(document, "select2-lastpos", {x: e.pageX, y: e.pageY});
+        lastMousePosition = {x: e.pageX, y: e.pageY};
     });
 
     /**
@@ -174,7 +174,7 @@
      */
     function installFilteredMouseMove(element) {
 	    element.bind("mousemove", function (e) {
-            var lastpos = $.data(document, "select2-lastpos");
+            var lastpos = lastMousePosition;
             if (lastpos === undefined || lastpos.x !== e.pageX || lastpos.y !== e.pageY) {
                 $(e.target).trigger("mousemove-filtered", e);
             }