Make <identifier> lowercase as per CodingGuidelines

*.c part for matches with '"[A-Z]+"'.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/merge.c b/builtin/merge.c
index a682043..7b0b4d5 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -194,7 +194,7 @@
 		"merge strategy to use", option_parse_strategy),
 	OPT_CALLBACK('X', "strategy-option", &xopts, "option=value",
 		"option for selected merge strategy", option_parse_x),
-	OPT_CALLBACK('m', "message", &merge_msg, "MESSAGE",
+	OPT_CALLBACK('m', "message", &merge_msg, "message",
 		"merge commit message (for a non-fast-forward merge)",
 		option_parse_message),
 	OPT__VERBOSITY(&verbosity),