_HasDropDown: problems on key repeat opening drop downs

[bill]

When using ENTER/SPACE key to open the drop down of a _HasDropDown based widget (ex: DropDownButton, ComboButton), there are problems if the user holds down the key long enough that it starts to repeat. It's because the popup is opened (and focus is shifted to the drop down) on keydown rather than keyup. Problems include:

• If the drop down is a Menu, or a TooltipDialog where first focus goes to a dijit.form.Button, the keyup event will "click" the menu's first option / dijit.form.Button, closing the menu / dialog (and doing some unwanted action)
• If the drop down is a TooltipDialog where the first field is an <input> / TextBox., it will insert spaces into that <input>/TextBox

[bill]

(In [24391]) Wait until onkeyup to focus popup widget, in order to avoid spurious onkeyup event to popup widget, or worse yet, if keys repeat, unwanted onkeydown events. Fixes #12698 on 1.6/.

[bill]

(In [24392]) Wait until onkeyup to focus popup widget, in order to avoid spurious onkeyup event to popup widget, or worse yet, if keys repeat, unwanted onkeydown events. Fixes #12698 on trunk !strict.