parse-opt: fake short strings for callers to believe in.

If we begin to parse -abc and that the parser knew about -a and -b, it
will fake a -c switch for the caller to deal with.

Of course in the case of -acb (supposing -c is not taking an argument) the
caller will have to be especially clever to do the same thing. We could
think about exposing an API to do so if it's really needed, but oh well...

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.h

@@ -119,6 +119,11 @@ enum {
 	PARSE_OPT_UNKNOWN,
 };
 
+/*
+ * It's okay for the caller to consume argv/argc in the usual way.
+ * Other fields of that structure are private to parse-options and should not
+ * be modified in any way.
+ */
 struct parse_opt_ctx_t {
 	const char **argv;
 	const char **out;