Added a try statement to catch the ImportError failure of the 'kill' function of the 'os' module.
This is a fix for bug #6841 (https://gna.org/bugs/?func=detailitem&item_id=6841) which was reported
by Daniel Perez in the post at https://mail.gna.org/public/relax-users/2006-09/msg00000.html
(Message-id: <44F7FFCF.4060102@...>).
This import statement fails under MS Windows as the 'kill' function is UNIX only.