fix(jqLite): mouseenter/-leave should not trigger on child elements

Mouseenter and mouseleave events were triggered on children of the
element they were bound to.
Change this to the expected behaviour, to only be triggered when
leaving/entering the actual element, not its children.

Closes angular#2131

src/jqLite.js

@@ -607,20 +607,20 @@ forEach({
 
       if (!eventFns) {
         if (type == 'mouseenter' || type == 'mouseleave') {
-          var counter = 0;
+          var entered = false;
 
           events.mouseenter = [];
           events.mouseleave = [];
 
           bindFn(element, 'mouseover', function(event) {
-            counter++;
-            if (counter == 1) {
+            if (!entered) {
+              entered = true;
               handle(event, 'mouseenter');
             }
           });
           bindFn(element, 'mouseout', function(event) {
-            counter --;
-            if (counter == 0) {
+            if (entered && indexOf(element.getElementsByTagName('*'), (event.toElement || event.relatedTarget)) === -1) {
+              entered = false;
               handle(event, 'mouseleave');
             }
           });

test/jqLiteSpec.js

@@ -798,8 +798,6 @@ describe('jqLite', function() {
         child.mouseover();
         expect(log).toEqual('parentEnter;childEnter;');
 
-        child.mouseout();
-        expect(log).toEqual('parentEnter;childEnter;');
         child.mouseout();
         expect(log).toEqual('parentEnter;childEnter;childLeave;');
         parent.mouseout();