pace() slept the entire rate-limit interval every call regardless of how
much of it had already elapsed since the last real send (e.g. spent
processing the previous block's response). Track the last send timestamp
and only sleep the remainder, recovering time already spent between
requests without changing the enforced minimum interval.
Verified against 10.0.0.129/10.0.0.254: multi-block /device/0 fetches
still complete cleanly, faster per sweep, with the same request spacing
guarantee (patch and measurement from QuiteYellow, PR #8 review).
Marc Billow
ff688f5d5d