parse-options: report uncorrupted multi-byte options

Because our command-line parser considers only one byte at the time
for short-options, we incorrectly report only the first byte when
multi-byte input was provided. This makes user-errors slightly
awkward to diagnose for instance under UTF-8 locale and non-English
keyboard layouts.

Report the whole argument-string when a non-ASCII short-option is
detected.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Improved-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -470,8 +470,11 @@ int parse_options(int argc, const char **argv, const char *prefix,
 	default: /* PARSE_OPT_UNKNOWN */
 		if (ctx.argv[0][1] == '-') {
 			error("unknown option `%s'", ctx.argv[0] + 2);
-		} else {
+		} else if (isascii(*ctx.opt)) {
 			error("unknown switch `%c'", *ctx.opt);
+		} else {
+			error("unknown non-ascii option in string: `%s'",
+			      ctx.argv[0]);
 		}
 		usage_with_options(usagestr, options);
 	}