OCTAVE_HELP vs HELP_OCTAVE

[Mike Miller]

Recent changes have been removing conditionals in the public API and
changing how they are defined when needed. This is good progress.

We now have a mix of macros of the form HAVE_OCTAVE_X and OCTAVE_HAVE_Y,
for example

  HAVE_OCTAVE_DEPRECATED_ATTR
  HAVE_OCTAVE_GUI

  OCTAVE_HAVE_FAST_INT_OPS
  OCTAVE_HAVE_SIG_JUMP

Can we pick one of these? Personally I would prefer all public symbols
to start with OCTAVE_.

-- 
mike