Because the proxy services changes to req params preferentially to live
data, if the client constantly changes the window (e.g due to spidering)
then it can accidentally stop the delivery of live events to the client
until the spidering process is complete. To help address this, we now
process live updates _even if_ we have some data to send to the client.
This is bounded in size to prevent the inverse happening: constantly
seeing new live events which starves changes to req params. This should
hopefully strike the right balance.
With regression test.
