(mac_compute_glyph_string_overhangs): Don't set

(mac_compute_glyph_string_overhangs): Don't set
overhangs unless the given glyph type is noncomposite CHAR_GLYPH.
[USE_CARBON_EVENTS] (mac_convert_event_ref): Convert dead key down
events.
(XTread_socket): Don't pass keyboard events with the option
modifier to the system when Vmac_command_key_is_meta is nil or
Vmac_option_modifier is non-nil.
[USE_CARBON_EVENTS] (read_socket_inev): New variable.
[USE_CARBON_EVENTS] (init_command_handler): Fix argument.
[USE_CARBON_EVENTS] (mac_handle_mouse_event): New Carbon event
handler function.
(install_window_handler) [USE_CARBON_EVENTS]: Install it.
(XTread_socket) [USE_CARBON_EVENTS]: Move mouse wheel event
handler part to mac_handle_mouse_event.