Why doesn't optparse.OptionParser.error() print the
list of correct options along with the error message
and usage?  This is what the user needs to know
whenever there's an error.  One can override this in a
subclass, but it's frustrating to have to do it every
time.  

To do this, change the first line in
OptionParser.error() from:

    self.print_usage(sys.stderr)

to:

    self.print_help(sys.stderr)
    print >>sys.stderr