git svn: fix authentication with 'branch'

Authentication fails with svn branch while svn rebase and
svn dcommit work fine without authentication failures.

$ git svn branch v7_3
Copying https://xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx at r27519
to https://xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/v7_3...
Can't create session: Unable to connect to a repository at URL
'https://xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx': No more
credentials or we tried too many times.
Authentication failed at
C:\Program Files\Git\mingw64/libexec/git-core\git-svn line 1200.

We add auth configuration to SVN::Client->new() to fix the issue.
Signed-off-by: NHiroshi Shirosaki <h.shirosaki@gmail.com>
Signed-off-by: NEric Wong <e@80x24.org>

git-svn.perl

@@ -1175,10 +1175,10 @@ sub cmd_branch {
 	::_req_svn();
 	require SVN::Client;
 
+	my ($config, $baton, undef) = Git::SVN::Ra::prepare_config_once();
 	my $ctx = SVN::Client->new(
-		config => SVN::Core::config_get_config(
-			$Git::SVN::Ra::config_dir
-		),
+		auth => $baton,
+		config => $config,
 		log_msg => sub {
 			${ $_[0] } = defined $_message
 				? $_message