roken: use strtok_r from roken

roken: use strtok_r from roken

Windows standard library doesn't provide strtok_r.  Use the strtok_r
that is provided from roken.

Change-Id: I1bccb9a306c9dd1963f044127fb5dfe4da5728cc
Reviewed-on: https://gerrit.openafs.org/13891
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>