[!TARGET_API_MAC_CARBON] Include Displays.h.

[!TARGET_API_MAC_CARBON] Include Displays.h.
(mac_screen_config_changed): New variable.
(mac_handle_dm_notification, init_dm_notification_handler)
(mac_get_screen_info): New functions.
[MAC_OS8] (main): Call init_dm_notification_handler.
(mac_initialize) [MAC_OSX]: Likewise.
(XTread_socket): Call mac_get_screen_info if screen config changed.
(mac_initialized): Make static.
(mac_initialize_display_info): Remove function.
(mac_term_init): Call mac_get_screen_info.  Add partial contents of
mac_initialize_display_info.