Revert "remove unused code"

This reverts commit 93f5e7508f.

select2.js

@@ -154,7 +154,26 @@
         });
     }
 
-     /**
+    /**
+     * filters mouse events so an event is fired only if the mouse moved.
+     *
+     * filters out mouse events that occur when mouse is stationary but
+     * the elements under the pointer are scrolled.
+     */    
+    function installFilteredMouseMove(element) {
+		var context = $(element[0].document);
+		context.on("mousemove", function (e) {
+	        context.data("select2-lastpos", {x: e.pageX, y: e.pageY});
+	    });
+        element.bind("mousemove", function (e) {
+            var lastpos = context.data("select2-lastpos");
+            if (lastpos === undefined || lastpos.x !== e.pageX || lastpos.y !== e.pageY) {
+                $(e.target).trigger("mousemove-filtered", e);
+            }
+        });
+    }
+
+    /**
      * Debounces a function. Returns a function that calls the original fn function only if no invocations have been made
      * within the last quietMillis milliseconds.
      *
@@ -403,6 +422,7 @@
             // initialize the container
             this.initContainer();
 
+            //installFilteredMouseMove(this.results);
             this.dropdown.delegate(resultsSelector, "mouseover", this.bind(this.highlightUnderEvent));
 
             installDebouncedScroll(80, this.results);