Display-related functions implemented from scratch. Add toolkit

Display-related functions implemented from scratch.  Add toolkit
scroll bars, mouse-sensitive mode line, help-echo, busy-cursor.
(x_calc_absolute_position): Subtract menu bar height
for YNegative, if using X toolkit.
(XTread_socket) [USE_MOTIF] <KeyPress>: Catch events
in scroll bars.
(SET_SAVED_MENU_EVENT): Give it statement form.
(XTflash): Don't flash the toolbar window.
(XTread_socket): Workaround for LessTif popup menus
in case of ButtonPress events.
(XTread_socket): Set inhibit_busy_cursor.