private functions in the core Octave distribution

[John W. Eaton]

I checked in the following change to make some internal plotting
functions private or to convert them to subfunctions (if possible).

  http://hg.savannah.gnu.org/hgweb/octave/rev/1aeb39118764

For now I've skipped the following plot functions that have internal
(i.e., __x__) names, for the reasons stated below.

Both of the following functions are used outside of the plot directory
so they can't be private to the plot directory alone.

  __next_line_color__.m
  __plt_get_axis_arg__.m

Some of the following __gnuplot_* functions might be useful for
debugging, so I left them alone for now.  For example, so we can ask
users to tell us "what does __gnuplot_version__ return on your
system?" or "what do you see for __gnuplot_has_feature__ (...)?".  But
I'm not sure we need to keep all of them available to users.  Is there
any need for __gnuplot_ginput__ or __gnuplot_open_stream__ to be
called directly?

  __gnuplot_get_var__.m
  __gnuplot_ginput__.m
  __gnuplot_has_feature__.m
  __gnuplot_open_stream__.m
  __gnuplot_version__.m

The __go_close_all__ function is called from C++, so as things work
now, it can't be private.

  __go_close_all__.m

As far as I can tell, both of the following functions could become
subfunctions of gnuplot_drawnow.  Is there any reason to not do that?

  __go_draw_axes__.m
  __go_draw_figure__.m

The following function is only called in isosurface.m, but it has a
complete doc string and might be useful by itself.  Is it intended to
be used directly by users?  If so, then we should rename it to
marching_cube.

  __marching_cube__.m

Is there any objection to more changes like this in other directories?

Comments?

jwe