Re-activate pl translation (fixes #56)

Author: jimwins

include/lib_proj_lang.inc.php

@@ -32,7 +32,7 @@
     'fr'    => 'French',
     'it'    => 'Italian',
     'ja'    => 'Japanese',
-#    'pl'    => 'Polish',
+    'pl'    => 'Polish',
     'pt_br' => 'Brazilian Portuguese',
 #    'ro'    => 'Romanian',
     'ru'    => 'Russian',