Show alternate menu panel on devices with menu key

Provide a softer transition to the overflow-everywhere world for
devices with menu keys. The panel menu will still be used on these
devices in response to a menu key press even in the presence of an
action bar with overflow.

Fix a few lingering bugs around dispatching the open-overflow
transition that caused problems with this along the way.

Change-Id: I9d77c70f6d15c47160ac06292984101d619c44e6