Ticket #2971: mouse click below non-droppeddown menubar activates menu box.

How to reproduce:
1. Switch the "Drop down menus" option off.
2. Press F9 to activate menubar. Menu is not dropped.
3. Click somewhere below menubar, on one of the files in the directory
listing.

Buggy behavior: the corresponding "Left" or "File" etc. dropdown is
opened, and the mouse button is released, menu item under the mouse
cursor is activated.

Correct behavior: clicking with the mouse somewhere other than the
active menubar doesn't open dropdown menu, instead removes the focus from
menubar and acts on the actual item under the mouse pointer (such
as a filename in the panel).

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>