(GC_CLIP_REGION): New macro.

(GC_CLIP_REGION): New macro.
(saved_port_clip_region): New variable.
(mac_begin_clip, mac_end_clip): New functions.
(XDrawLine, mac_erase_rectangle, mac_draw_bitmap, XFillRectangle)
(mac_draw_rectangle, mac_draw_string_common, mac_copy_area)
(mac_copy_area_with_mask, mac_scroll_area): Use them.
(mac_set_clip_rectangle, mac_reset_clipping): Remove functions.
[USE_ATSUI] (atsu_get_text_layout_with_text_ptr)
[MAC_OS_X_VERSION_MAX_ALLOWED < 1020]: Specify kATSLineFractDisable.
(mac_draw_string_common) [MAC_OSX && USE_ATSUI]: Clip to clipping
rectangles stored in gc.
(XFreeGC): Dispose clipping region.
(mac_set_clip_rectangles, mac_reset_clip_rectangles): New functions.
(x_draw_fringe_bitmap, x_set_glyph_string_clipping)
(x_draw_relief_rect, x_draw_box_rect, x_draw_stretch_glyph_string)
(x_draw_glyph_string, x_clip_to_row, x_draw_hollow_cursor)
(x_draw_bar_cursor): Use them.
(x_set_glyph_string_clipping): Use get_glyph_string_clip_rects to
get multiple clipping rectangles.