The following changes consolidate code related to writing and

The following changes consolidate code related to writing and
inserting glyphs, exposing frame, the tool bar, the mouse face,
the output cursor, and help echo from xterm.c, w32term.c and
macterm.c into xdisp.c.  It also generalizes the use of the
window_part enum instead of using numeric values throughout.

* xdisp.c: Consolidate gui-independent code here.
Include keymap.h.
(Qhelp_echo): Import.
(mouse_autoselect_window, x_stretch_cursor_p): Declare here.
(help_echo_string, help_echo_window, help_echo_object)
(previous_help_echo_string, help_echo_pos): Declare here.
(output_cursor, last_mouse_frame, last_tool_bar_item): Declare here.
(estimate_mode_line_height): Define here.  Handle windowing
systems directly (without using estimate_mode_line_height_hook).
(x_y_to_hpos_vpos, get_tool_bar_item, note_tool_bar_highlight):
(update_window_cursor, update_cursor_in_window_tree)
(fast_find_position, fast_find_string_pos)
(note_mode_line_highlight, note_mode_line_or_margin_highlight)
(expose_area, expose_line, expose_overlaps, expose_window)
(expose_window_tree, phys_cursor_in_rect_p): New generic versions;
declared static as they are only used locally in xdisp.c.
(draw_glyphs): Rename from x_draw_glyphs and make static.
(tool_bar_item_info, notice_overwritten_cursor): Make static.
(frame_to_window_pixel_xy, get_glyph_string_clip_rect)
(set_output_cursor, x_cursor_to, handle_tool_bar_click)
(x_write_glyphs, x_insert_glyphs, x_clear_end_of_line):
(x_fix_overlapping_area, draw_phys_cursor_glyph, erase_phys_cursor)
(display_and_set_cursor, x_update_cursor, x_clear_cursor)
(show_mouse_face, clear_mouse_face, cursor_in_mouse_face_p)
(note_mouse_highlight, x_clear_window_mouse_face)
(cancel_mouse_face, x_draw_vertical_border, expose_frame)
(x_intersect_rectangles): New generic functions for use by xdisp.c
and GUI front-ends.
(syms_of_xdisp): Initialize and staticpro help_echo* variables.
Defvar_bool "x-streach-cursor" and "mouse-autoselect-window" here.