i18n: factorize "invalid value" messages

Use the same message when an invalid value is passed to a command line
option or a configuration variable.

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/am.c b/builtin/am.c
index b6be1f1..97dbeb8 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -199,7 +199,7 @@ static int am_option_parse_empty(const struct option *opt,
 	else if (!strcmp(arg, "keep"))
 		*opt_value = KEEP_EMPTY_COMMIT;
 	else
-		return error(_("Invalid value for --empty: %s"), arg);
+		return error(_("invalid value for '%s': '%s'"), "--empty", arg);
 
 	return 0;
 }
@@ -2239,7 +2239,8 @@ static int parse_opt_patchformat(const struct option *opt, const char *arg, int
 	 * when you add new options
 	 */
 	else
-		return error(_("Invalid value for --patch-format: %s"), arg);
+		return error(_("invalid value for '%s': '%s'"),
+			     "--patch-format", arg);
 	return 0;
 }
 
@@ -2282,7 +2283,8 @@ static int parse_opt_show_current_patch(const struct option *opt, const char *ar
 				break;
 		}
 		if (new_value >= ARRAY_SIZE(valid_modes))
-			return error(_("Invalid value for --show-current-patch: %s"), arg);
+			return error(_("invalid value for '%s': '%s'"),
+				     "--show-current-patch", arg);
 	}
 
 	if (resume->mode == RESUME_SHOW_PATCH && new_value != resume->sub_mode)