Populate 'bufh' in get responses

This forms the basis of "Futures" for gets

Change-Id: Ifec6416601b489eb3151a69f098910535d217c8e
Reviewed-on: http://review.couchbase.org/38982
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>