(HAVE_DIALOGS): Define if TARGET_API_MAC_CARBON.

(HAVE_DIALOGS): Define if TARGET_API_MAC_CARBON.
(mac_handle_dialog_event, install_dialog_event_handler)
(create_and_show_dialog) [TARGET_API_MAC_CARBON]: New functions.
(DIALOG_LEFT_MARGIN, DIALOG_TOP_MARGIN, DIALOG_RIGHT_MARGIN)
(DIALOG_BOTTOM_MARGIN, DIALOG_MIN_INNER_WIDTH)
(DIALOG_MAX_INNER_WIDTH, DIALOG_BUTTON_BUTTON_HORIZONTAL_SPACE)
(DIALOG_BUTTON_BUTTON_VERTICAL_SPACE, DIALOG_BUTTON_MIN_WIDTH)
(DIALOG_TEXT_MIN_HEIGHT, DIALOG_TEXT_BUTTONS_VERTICAL_SPACE)
(DIALOG_ICON_WIDTH, DIALOG_ICON_HEIGHT, DIALOG_ICON_LEFT_MARGIN)
(DIALOG_ICON_TOP_MARGIN) [TARGET_API_MAC_CARBON]: New macros.
(mac_dialog) [TARGET_API_MAC_CARBON]: Remove function.
(mac_dialog_show) [TARGET_API_MAC_CARBON]: Use create_and_show_dialog.