Issue 241 withdrew seven consumers in one pass; 0.1.10 refuses a file it
cannot read, and a file read whole that names nobody still withdrew
everybody. A pass that would withdraw more than withdrawAtOnce consumers
(1), or more than withdrawFraction (0.5) of those held, now withdraws
nothing and says so; while the mesh goes on not asking, one is let go every
releaseEveryMs (an hour). A consumer asked for again is kept.
jochen