showing the menu. This makes the "Most recently used" menu more accurate.
(menu-bar-update-buffers): The frame list is now an integrated
part of the buffer menu.
(msb--few-menus, msb--very-many-menus): Added rmail-edit-mode.
Split big menus into sub-menus.
(msb-max-menu-items): Changed default value. This variable
now depicts the maximum number of items in a sub-menu.
(msb-display-most-recently-used): Changed default value.
(mouse-select-buffer): Now handles several levels of
sub-menus. New format on return value.
