parse-options: typo check for unknown switches

parse-options: typo check for unknown switches

The user specifies a long option but forgets to type the second
leading dash, we currently detect and report that fact if its first
letter is a valid short option. This is done for safety, to avoid
ambiguity between short options (and their arguments) and a long
option with a missing dash.

This diagnostic message is also helpful for long options whose first
letter is not a valid short option, however. Print it in that case,
too, as a courtesy.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>