Throw ArgumentError when dict is passed to get

To be more precise, we accept dicts for get, but values must be integers
which are TTLs (i.e. touch)

Change-Id: I8d5f7ab07885f2450c7e5a65fb96262cc696400a
Reviewed-on: http://review.couchbase.org/26328
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>