(check_x): Fix error message.

(check_x): Fix error message.

(x_set_menu_bar_lines): New function, copied from xfns.c.
(IT_set_frame_parameters): Use selected_frame instead of
the_only_frame.
(internal_terminal_init): Use selected_frame instead of the_only_frame.
(check_x): New function, replacing macro in msdos.h.
(XMenuActivate): Use selected_frame instead of
the_only_frame.  Don't let the title for the "Buffers" popup
include a number when it is split into several menus.