GtkMenuShell::select_item
select_item() is largely
used internally. A 'selected' item is displayed in the prelight
state and has its submenu popped up, if it has one. This is also
achieved by using the mouse pointer or arrow keys in an active
GtkMenu, and should not be confused with
the "activate" signal, which
is triggered by mouse clicks or the Enter key.
Using this method causes the designated item to emit the
"select" signal, which in turn
triggers the 'selected' state.