Further clean-up: usage() vs die()

This hopefully finishes the clean-up Ramsay started with recent
commit 15e593e4d3 and commit
8cdf33643d.

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-check-ref-format.c

@@ -9,6 +9,6 @@
 int cmd_check_ref_format(int argc, const char **argv, const char *prefix)
 {
 	if (argc != 2)
-		usage("git check-ref-format refname");
+		usage("git-check-ref-format refname");
 	return !!check_ref_format(argv[1]);
 }