Glib option parsing

[Jonathon Jongsma <jonathon jongsma gmail com>]

Up til now I've only used really basic commandline parsing with Glib,
but now I'm playing around with something a bit more involved. 
Basically I want to provide a bunch of commandline switches and then
also require one extra argument.  For example, the format for the
command should be:

programname [OPTIONS] output_filename

If the user doesn't provide the output_filename argument, I want the
program to print the help text (i.e. the same thing that you get
automatically from Glib::OptionContext when you use the --help option)
and then exit.  But I don't see any way to manually display this help
text.  Is this possible?

Jonathon