Send pending requests before waiting for responses

[dpkp]

I don't think it is strictly necessary to send before receiving in the poll loop, but I think the design makes more sense. Leveraging the request-time-out loop was more of an optimization to avoid looping through the connection list twice. In the future we might consider other optimizations, including tracking connections w/ pending data to write and using select to identify which/when those sockets are available for writing.

---

This change is