Sequence numbers for requests

[trishume]

In theory this is slightly better since even if requests are outdated you still see stuff change as you are typing which makes stuff look more responsive. The code is also cleaner.

However I think in practice it might be slower since it continues to transfer data from the previous requests with bandwidth it could be using to read other requests.

I'm going to leave this sitting here unmerged in case we want it later.

@mmailhot