NCBC-716: IBucket.Replace overload has wrong type for CAS

Change-Id: I59a4daf9f71c3d277e886699c513101928a9ee5a
Reviewed-on: http://review.couchbase.org/42856
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Jeffry Morris <jeffrymorris@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>