Fix problem where opening one drop down does not close the previous.
Fix problem where opening one drop down does not close the previous.

When clicking the second button (to open the second dropdown),
FormElement::_onMouse() was squelching the mousedown event,
which prevented dijit.util.popup from hearing it and closing
the first popup.

Refs #3474.

There's still a problem (on IE, at least) if you alternate back and forth
between the Edit button and Save button.  dijit.util.focus is trying to
call menu.close() which doesn't exist.  Need to rearchitect that code.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@9255 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful