svn: prevent hanging when reading output from pipes

This occurs even on non-windows machines.

Fixed by opening STDERR in append mode, as per
http://php.net/manual/en/function.proc-open.php#97012

Fixes #254

Author: FSD-Christian-ADM

SourceSVN/SourceSVN.php

@@ -324,7 +324,7 @@ private function svn_run( $p_cmd, $p_repo = null )
 
 		$t_svn_proc = proc_open(
 			$t_svn_cmd,
-			array( array( 'pipe', 'r' ), array( 'pipe', 'w' ), array( 'pipe', 'w' ) ),
+			array( array( 'pipe', 'r' ), array( 'pipe', 'w' ), array( 'pipe', 'a' ) ),
 			$t_pipes
 		);