JCBC-417: Expose (async)getsFromReplica.

This changeset exposes the same replica read functionality as before,
but this time also exposes its underlying CASValue. The signature is
a mix between a replica get and a gets operation.

Change-Id: Id094092280115e66af6962eb8898a6e4b5f27f78
Reviewed-on: http://review.couchbase.org/33884
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>