Fix hangs when clicking on Haiku menu bar to activate frame

Fix hangs when clicking on Haiku menu bar to activate frame

* src/haiku_io.c (haiku_len): Handle new event `MENU_BAR_CLICK'.
* src/haiku_support.cc (class EmacsWindow): Remove most of the
menu bar cv stuff.
(MessageReceived): Handle REPLAY_MENU_BAR message.
(EmacsWindow_signal_menu_update_complete): Delete function.
(be_replay_menu_bar_event): New function.

* src/haiku_support.h (enum haiku_event_type): New event type
`MENU_BAR_CLICK'.
(struct haiku_menu_bar_click_event): New struct.

* src/haikumenu.c (haiku_activate_menubar): New function.
* src/haikuterm.c (haiku_read_socket): Save a
MENU_BAR_ACTIVATE_EVENT and the menu bar click event instead of
handling the menu bar update synchronously.
(haiku_create_terminal): Set `activate_menubar_hook'.
(syms_of_haikuterm): Remove extraneous newline.

* src/haikuterm.h (struct haiku_output): New field
`saved_menu_event'.