SPY-135: Expose asyncCAS with Expiration and default transcoder.

Change-Id: I99ecf0b293a9d52871b81e9166f07a35f90c712a
Reviewed-on: http://review.couchbase.org/29346
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>