sys was used (line 268) but not imported. Just import it

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@19644 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Document.py

@@ -26,7 +26,7 @@
 #
 ##############################################################################
 
-import re, socket
+import re, socket, sys
 from DateTime import DateTime
 from operator import add
 from xmlrpclib import Fault