Refactor: Use cookie.sendResponse in ArithmeticContext
Refactor: Use cookie.sendResponse in ArithmeticContext

sendResponse will try to fit the response packet within the
already allocated output buffer, instead of allocating a new
buffer for the output message.

Change-Id: I5f9c63098067a3683961dd28091962a8e0929290
Reviewed-on: http://review.couchbase.org/85731
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine