Event: Normalize mouse event properties in drag events

DragEvent is a superset of MouseEvent, so we want to fix up mouse
properties like pageX and pageY.

Fixes gh-1925

src/event.js

@@ -14,7 +14,7 @@ define([
 
 var
 	rkeyEvent = /^key/,
-	rmouseEvent = /^(?:mouse|pointer|contextmenu)|click/,
+	rmouseEvent = /^(?:mouse|pointer|contextmenu|drag)|click/,
 	rfocusMorph = /^(?:focusinfocus|focusoutblur)$/,
 	rtypenamespace = /^([^.]*)(?:\.(.+)|)/;