Added simple test implementation of tftpserver

Renamed lib/tftpserver.php to lib/tftp.php
Fixed error output from lib/tftp.php

Note: current simple tftpserver.php test implementation stores/read files
from memory (not fs). So you need to put a file, before you can get that
file back.

Signed-off-by: Diederik de Groot <ddegroot@talon.nl>

lib/tftp.php

@@ -612,7 +612,10 @@ class TFTPServer {
 
     while(true) {
       $read = array($this->_socket);
-      $r = stream_select($read, $write = null, $excpt = null, 1);
+      //$r = stream_select($read, $write = null, $excpt = null, 1);
+      $write = null;
+      $except = null;
+      $r = stream_select($read, $write, $excpt, 1);
 
       if($r === false) {
 	$this->log_error("server", "select returned false");