Let callers provide their own handler for the short option -h even
without the flag PARSE_OPT_NO_INTERNAL_HELP, but call the internal
handler (showing usage information) if that is the only parameter.
Implement the first part by checking for -h only if parse_short_opt()
can't find it and returns -2.
Signed-off-by: NRene Scharfe <l.s.r@web.de>
Signed-off-by: NJeff King <peff@peff.net>