view_iterator_t: use xrange from _pyport

Py3 doesn't have xrange

Change-Id: I4001a1e21779b17356a565b164f0e1ac3ce9a2ca
Reviewed-on: http://review.couchbase.org/29729
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>