Event: Add a note about a mouseenter bug in Chrome

Also, add a support comment about older Safari.

Refs https://code.google.com/p/chromium/issues/detail?id=333868
Partially cherry-picked from a5e1c9b44c971fd7046d9a95bd0810e50840b663

src/event.js

@@ -782,6 +782,14 @@ jQuery.Event.prototype = {
 };
 
 // Create mouseenter/leave events using mouseover/out and event-time checks
+// so that event delegation works in jQuery.
+// Do the same for pointerenter/pointerleave and pointerover/pointerout
+// Support: Safari<7.0
+// Safari doesn't support mouseenter/mouseleave at all.
+// Support: Chrome 40+
+// Mouseenter doesn't perform while left mouse button is pressed
+// (and initiated outside the observed element)
+// https://code.google.com/p/chromium/issues/detail?id=333868
 jQuery.each({
 	mouseenter: "mouseover",
 	mouseleave: "mouseout",