(XTread_socket) <FocusIn>: Queue a FOCUS_IN_EVENT which

(XTread_socket) <FocusIn>: Queue a FOCUS_IN_EVENT which
will be translated to a switch-frame event in when reading the
event queue.  This is necessary because Emacs otherwise won't
perform a switch-frame to a new frame until some other event, for
example a keystroke event, forces it to do so.  This has various
effects, one visible being that the cursor of a frame created with
C-x 5 2 or switched to with a window manager key binding like
A-TAB stays hollow because selected_window isn't on the newly
focused frame until the switch-frame is performed.