It seems that the paperwork side of things is complete.  In the meantime
I've updated the Haiku patch with support for some new features, such as
double buffering and Cairo drawing support, and a new Haiku appendix in
the manual.

Right now the Cairo support is only used for font rendering, but that
could also change.

There are a couple warts I can think of presently, including the "fix"
in floatfns.c to double_integer_scale to work around some problems in
the Haiku C library, pcpu calculation in sysdep.c, and how Cairo drawing
works (or rather, doesn't work) when double buffering is disabled.

There's also the bidi crash from earlier, but I haven't seen that
afterwards, and one thread-related crash has probably been fixed, but I
can't be sure about.

A recent version of the patch is attached below, if someone could review
it it would be greatly appreciated.  Thanks.