Delete old session files, suggested by Torben Nehmer, see bug oc-736

lib/user.php

@@ -200,7 +200,7 @@ class OC_User {
 		if( $run ){
 			$uid=self::checkPassword( $uid, $password );
 			if($uid){
-				session_regenerate_id();
+				session_regenerate_id(true);
 				self::setUserId($uid);
 				OC_Hook::emit( "OC_User", "post_login", array( "uid" => $uid, 'password'=>$password ));
 				return true;