prototype: Make sure Element#observe is always chainable.

CHANGELOG

@@ -1,6 +1,6 @@
 *SVN*
 
-* Make sure Element#stopObserving is always chainable.  [sam]
+* Make sure Element#observe and Element#stopObserving are always chainable.  [sam]
 
 * Event.fire/Element#fire now returns the newly-fired event instead of the event's target element.  [sam]
 

src/event.js

@@ -170,7 +170,7 @@ Object.extend(Event, (function() {
       var id = getEventID(element), name = getDOMEventName(eventName);
       
       var wrapper = createWrapper(id, eventName, handler);
-      if (!wrapper) return false;
+      if (!wrapper) return element;
       
       if (element.addEventListener) {
         element.addEventListener(name, wrapper, false);

test/unit/event.html

@@ -183,15 +183,22 @@
       assertEqual(0, Event.cache[eventID].somethingHappened.length);
     }},
     
-    testStopObservingIsChainable: function() { with(this) {
+    testObserveAndStopObservingAreChainable: function() { with(this) {
       var span = $("span"), observer = function() { };
-      span.observe("somethingHappened", observer);
+
+      assertEqual(span, span.observe("somethingHappened", observer));
       assertEqual(span, span.stopObserving("somethingHappened", observer));
+
       span.observe("somethingHappened", observer);
       assertEqual(span, span.stopObserving("somethingHappened"));
+
       span.observe("somethingHappened", observer);
       assertEqual(span, span.stopObserving());
       assertEqual(span, span.stopObserving()); // assert it again, after there are no observers
+
+      span.observe("somethingHappened", observer);
+      assertEqual(span, span.observe("somethingHappened", observer)); // try to reuse the same observer
+      span.stopObserving();
     }},
     
     testDocumentContentLoadedEventFiresBeforeWindowLoad: function() { with(this) {