Improve tracking of modified regions on Haiku

Improve tracking of modified regions on Haiku

* src/haiku_support.cc (class EmacsView): New field
`invalid_region'.
(FlipBuffers): Only invalidate that region.
(SetUpDoubleBuffering): Clear that region.
(BView_draw_lock): New parameters for denoting the region
to invalidate.
(BView_invalidate_region): New function.
* src/haiku_support.h: Update prototypes.
* src/haikufns.c (haiku_set_background_color):
* src/haikumenu.c (digest_menu_items):
* src/haikuterm.c (haiku_clip_to_string):
(haiku_flip_buffers):
(haiku_clear_frame_area):
(haiku_clear_frame):
(haiku_draw_glyph_string):
(haiku_after_update_window_line):
(haiku_draw_window_cursor):
(haiku_draw_vertical_window_border):
(haiku_draw_window_divider):
(haiku_draw_fringe_bitmap):
(haiku_scroll_run):
(haiku_read_socket):
(haiku_flash):
(haiku_clear_under_internal_border): Mark appropriate region as
invalid before buffer flip.