g = g_delete (g) - Delete a gnuplot_object and its directory
g_delete () Delete all gnuplot_object directories
g_delete ("all") Delete all gnuplot_object directories
g_delete ("siblings") Delete all gnuplot_object directories created
by this octave process
TODO: A mechanism to make sure no directories are forgotten (disk
leaks, as in "memory leaks") and that no dir gets deleted spuriously
(that side is ok now. Just do g_delete() now and then).