Allow non-system tooltips to display above menus on Haiku

Allow non-system tooltips to display above menus on Haiku

* doc/emacs/haiku.texi (Haiku Basics): Document that tooltips
can now be displayed above the menu bar.

* lisp/tooltip.el (tooltip-show-help): Only display help text in
the echo area if Haiku system tooltips are enabled.

* src/haiku_support.cc (FlipBuffers): Stop flushing view.
* src/haikufns.c (Fx_show_tip): Fix a sizing bug leading to
tooltips needing two redisplays to display correctly.
* src/haikuterm.c (haiku_read_socket): Ignore resize events on
tooltips.