Fixing bug 373687. Reduce the potential for misunderstanding...

Fixing bug 373687. Reduce the potential for misunderstanding nsEventDispatcher::Dispatch. r=olli.pettay@gmail.com

content/events/public/nsEventDispatcher.h

@@ -202,6 +202,8 @@ public:
    * retargeting) and the originalTarget of the DOM Event.
    * aTarget is always used as the starting point for constructing the event
    * target chain, no matter what the value of aEvent->target is.
+   * In other words, aEvent->target is only a property of the event and it has
+   * nothing to do with the construction of the event target chain.
    * Neither aTarget nor aEvent is allowed to be nsnull.
    * @note Use this method when dispatching an nsEvent.
    */