Header sync used to run when complete (right count of blocks
received) or every 10 sec regardless. Sometimes 10 secs is not
enough, especially when a big batch of blocks bodies is arriving
at the same time.
This tweaks the time-based heuristic just a bit to only ask for
headers when stalled, meaning that the header head has not
*progressed* for 10 seconds.
* Fix bad header sync timeout logic
* Improve stability of fast sync test
Adds regular pings so that the 2 test servers know each others'
heights (necessary to find most work peer). Stop mining on the
first server once the 2nd kicks in. Avoids chasing a fast moving
target on Cuckoo10.
Ignotus Peverell
9554f93e1d