Adds support for get-and-lock and unlock.

Get and lock works as expected, but unlock hangs.

Change-Id: I3bc07ff968954ebd716895d529a962f4fdc5a24f
Reviewed-on: http://review.couchbase.org/25816
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>