NCBC-711: Add support for GetL, Unlock and provide GetWithLock impl on IBucket

Change-Id: Ibd33d0ece5bf7408f0d4291408c9c1b1821b5f19
Reviewed-on: http://review.couchbase.org/42912
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Jeffry Morris <jeffrymorris@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>