(mac_draw_line, mac_draw_line_to_pixmap): Adjust
endpoints of strictly horizontal/vertical lines.
(mac_set_clip_rectangles) [USE_CG_DRAWING]: Set clip_rects.
(pcm_init, pcm_get_status): New functions.
(x_per_char_metric, XLoadQueryFont): Use them instead of
XCharStructRow and related macros.
(x_draw_relief_rect): Don't adjust arguments of mac_draw_line.
(x_free_frame_resources) [TARGET_API_MAC_CARBON]: Free FRAME_FILE_NAME.
(XTread_socket) [TARGET_API_MAC_CARBON]: Handle proxy icon drag
and window path pop-up menu on title bar.
(mac_use_core_graphics) [USE_CG_DRAWING]: Set default to 1.