ondijitclick and _HasDropDown incompatibility

[bill]

Putting an ondijitclick handler on a node for a widget that extends _HasDropDown doesn't work. The problem is that ondijitclick calls dojo.stopEvent(e) on the keyDown event:

d.stopEvent(e);		// stop event to prevent scrolling on space key in IE

That stopEvent() is from #3942. It prevents the connect in _HasDropDown from firing:

this.connect(this._buttonNode, "onkeydown", "_onDropDownKeydown");

(Discovered this while working on #11003.)

[bill]

(In [21892]) dojo.stopEvent() prevents dojo.connect()'d handlers from seeing the onkeydown event; use preventDefault() instead. preventDefault() still solves the problem where IE scrolls on space bar. Fixes #11007, refs #3942 !strict.