Before we hardcoded popdowns to only button 1 before. But we need
to actually pop down on the release of the activating button.
(Once the button is released, if the we don't pop-down the menu,
then subsequently we let the user use any button.)
https://bugzilla.gnome.org/show_bug.cgi?id=596371
When the user click+hold+release over the icon, the effect we want
is for the menu to stick around.
Also, allow the user to mouse over the actual windows and select
them directly. If the user mouses over a window, reflect that in
the menu.
https://bugzilla.gnome.org/show_bug.cgi?id=594699
Callers will generally expect _popup and _popdown to be a no-op if
the menu is already in that state; make it so.
Also change the 'popdown' signal to be 'cancelled'; this is
clearer and allows us to avoid having activate also call popdown.
https://bugzilla.gnome.org/show_bug.cgi?id=594699
When the user click+hold+release over the icon, the effect we want
is for the menu to stick around.
Also, allow the user to mouse over the actual windows and select
them directly. If the user mouses over a window, reflect that in
the menu.
