gitweb: Use git-show-ref instead of git-peek-remote

Use "git show-ref --dereference" instead of "git peek-remote
$projectroot/project" in git_get_references. git-show-ref is faster
than git-peek-remote (40ms vs 56ms user+sys for git.git repository);
even faster is reading info/refs file (if it exists), but the
information in info/refs can be stale; that and the fact that
info/refs is meant for dumb protocol transports, not for gitweb.

git-show-ref is available since v1.4.4; the output format is slightly
different than git-peek-remote output format, but we accept both.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -1154,14 +1154,15 @@ sub git_get_last_activity {
 sub git_get_references {
 	my $type = shift || "";
 	my %refs;
-	# 5dc01c595e6c6ec9ccda4f6f69c131c0dd945f8c	refs/tags/v2.6.11
-	# c39ae07f393806ccf406ef966e9a15afc43cc36a	refs/tags/v2.6.11^{}
-	open my $fd, "-|", $GIT, "peek-remote", "$projectroot/$project/"
+	# 5dc01c595e6c6ec9ccda4f6f69c131c0dd945f8c refs/tags/v2.6.11
+	# c39ae07f393806ccf406ef966e9a15afc43cc36a refs/tags/v2.6.11^{}
+	open my $fd, "-|", git_cmd(), "show-ref", "--dereference",
+		($type ? ("--", "refs/$type") : ()) # use -- <pattern> if $type
 		or return;
 
 	while (my $line = <$fd>) {
 		chomp $line;
-		if ($line =~ m/^([0-9a-fA-F]{40})\trefs\/($type\/?[^\^]+)/) {
+		if ($line =~ m!^([0-9a-fA-F]{40})\srefs/($type/?[^^]+)!) {
 			if (defined $refs{$1}) {
 				push @{$refs{$1}}, $2;
 			} else {