refs: use warning() instead of fprintf(stderr, "warning: ")

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -996,7 +996,7 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
 
 	err = unlink(git_path("logs/%s", lock->ref_name));
 	if (err && errno != ENOENT)
-		fprintf(stderr, "warning: unlink(%s) failed: %s",
+		warning("unlink(%s) failed: %s",
 			git_path("logs/%s", lock->ref_name), strerror(errno));
 	invalidate_cached_refs();
 	unlock_ref(lock);
@@ -1438,8 +1438,7 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
 				if (get_sha1_hex(rec + 41, sha1))
 					die("Log %s is corrupt.", logfile);
 				if (hashcmp(logged_sha1, sha1)) {
-					fprintf(stderr,
-						"warning: Log %s has gap after %s.\n",
+					warning("Log %s has gap after %s.",
 						logfile, show_date(date, tz, DATE_RFC2822));
 				}
 			}
@@ -1451,8 +1450,7 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
 				if (get_sha1_hex(rec + 41, logged_sha1))
 					die("Log %s is corrupt.", logfile);
 				if (hashcmp(logged_sha1, sha1)) {
-					fprintf(stderr,
-						"warning: Log %s unexpectedly ended on %s.\n",
+					warning("Log %s unexpectedly ended on %s.",
 						logfile, show_date(date, tz, DATE_RFC2822));
 				}
 			}