git-svn: fix git svn info to work without arguments

commit 2fe403e745 broke "git-svn info ."
due to replacing '.' with '' in canonicalize_path for the top directory,
while find_file_type_and_diff_status was not corrected.

Bug reports:

http://thread.gmane.org/gmane.comp.version-control.git/87822/
http://bugs.debian.org/490400

Signed-off-by: Dmitry Potapov <dpotapov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -1226,7 +1226,7 @@ sub linearize_history {
 
 sub find_file_type_and_diff_status {
 	my ($path) = @_;
-	return ('dir', '') if $path eq '.';
+	return ('dir', '') if $path eq '';
 
 	my $diff_output =
 	    command_oneline(qw(diff --cached --name-status --), $path) || "";