PYCBC-261: Append/prepend don't support TTL

Change-Id: Id134b2e4262bebc4d2c7361c85c2d8f8e9b5c88c
Reviewed-on: http://review.couchbase.org/42351
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>