git-svn: reduce stat() calls for a backwards compatibility check

Also, this fixes a bug where in an odd case a remote named
"config" could get renamed to ".metadata".
Signed-off-by: NEric Wong <normalperson@yhbt.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -1457,7 +1457,7 @@ sub tmp_config {
 	my (@args) = @_;
 	my $old_def_config = "$ENV{GIT_DIR}/svn/config";
 	my $config = "$ENV{GIT_DIR}/svn/.metadata";
-	if (-e $old_def_config && ! -e $config) {
+	if (! -f $config && -f $old_def_config) {
 		rename $old_def_config, $config or
 		       die "Failed rename $old_def_config => $config: $!\n";
 	}