PYCBC-262, PYCBC-263: Fix documented exceptions on locked items

Change-Id: I28bfff6f202d41f9f01750bf4b20bc9698bf9dcd
Reviewed-on: http://review.couchbase.org/42353
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>