cvsserver: Add support for packed refs

req_update still parses /refs/heads manually. Replace this by
a call to show-ref.
Signed-off-by: NLars Noschinski <lars@public.noschinski.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-cvsserver.perl

@@ -947,21 +947,15 @@ sub req_update
     # projects (heads in this case) to checkout.
     #
     if ($state->{module} eq '') {
-	my $heads_dir = $state->{CVSROOT} . '/refs/heads';
-	if (!opendir HEADS, $heads_dir) {
-	    print "E [server aborted]: Failed to open directory, "
-	      . "$heads_dir: $!\nerror\n";
-	    return 0;
-	}
+        my $showref = `git show-ref --heads`;
         print "E cvs update: Updating .\n";
-	while (my $head = readdir(HEADS)) {
-	    if (-f $state->{CVSROOT} . '/refs/heads/' . $head) {
-	        print "E cvs update: New directory `$head'\n";
-	    }
-	}
-	closedir HEADS;
-	print "ok\n";
-	return 1;
+        for my $line (split '\n', $showref) {
+            if ( $line =~ m% refs/heads/(.*)$% ) {
+                print "E cvs update: New directory `$1'\n";
+            }
+        }
+        print "ok\n";
+        return 1;
     }