Dialog: stacks calls to focus() on dialog hide

[bill]

Apparently every time that you open then close a dialog, it calls

this.connect(this._fadeOut,"onEnd",dojo.hitch(dijit,"focus",this._savedFocus));

and never disconnects... which means that after showing a dialog multiple times and then closing it, focus will be sent to many places on the screen (though ending up at the correct place).

Not sure if there's an actual bug here (maybe just that things slow down), but I want to fix the design problem.

[bill]

(In [18869]) Fix bug where every time a Dialog was hidden it would create a new conect, thus calling focus n times (where n is the number of times the dialog was previously hidden). Fixes #9563.