Popupmenu: update item under mouse upon press

We need to update item under mouse when doing a mouse press
since you don't have a guarantee that there will be a mouse
move before you eventually get a mouse release. This will
be the case on iOS (and probably other touch platforms).

Change-Id: Ia7220e9a822248ee7dc73b5530b04e858a0be47b
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>