fix($animate): avoid hanging animations if the active CSS transition class is missing

Closes #4732
Closes #4490

css/angular.css

@@ -9,3 +9,14 @@
 ng\:form {
   display: block;
 }
+
+/* The styles below ensure that the CSS transition will ALWAYS
+ * animate and close. A nasty bug occurs with CSS transitions where
+ * when the active class isn't set, or if the active class doesn't
+ * contain any styles to transition to, then, if ngAnimate is used,
+ * it will appear as if the webpage is broken due to the forever hanging
+ * animations. The clip (!ie) and zoom (ie) CSS properties are used
+ * since they trigger a transition without making the browser
+ * animate anything and they're both highly underused CSS properties */
+.ng-animate { clip:rect(1px, auto, auto, 0); -ms-zoom:1.0001; }
+.ng-animate-active { clip:rect(0, auto, auto, 0); -ms-zoom:1; }