Update copyright year.

Update copyright year.
(mac_store_apple_event): Change return type to void in extern.
(mac_handle_apple_event): Don't get return value from
mac_store_apple_event.
[TARGET_API_MAC_CARBON] (Vmac_dnd_known_types): New variable.
(syms_of_macselect) [TARGET_API_MAC_CARBON]: Defvar it.
[TARGET_API_MAC_CARBON] (mac_do_track_drag): Move function from
macterm.c.  Use Vmac_dnd_known_types as acceptable flavors.
[TARGET_API_MAC_CARBON] (mac_do_receive_drag): Likewise.  New
implementation using create_apple_event_from_drag_ref.
[TARGET_API_MAC_CARBON] (mac_do_track_dragUPP)
(mac_do_receive_dragUPP): Move variables from macterm.c.
(install_drag_handler, remove_drag_handler): New functions.