Try a refused stream again when its try is gone

A sender whose stream the receiver refuses sends one packet of records
a wait, and the refusal is over when that packet is acknowledged with
no REFUSED. When the try itself went to no one (the receiver started
again, as a node upgraded one after the other does, or the path lost
it) nothing acknowledged it: the sender took its epoch for lost, began
another, and then sent nothing more, still waiting on the try, with no
record in flight to probe for. Two nodes of a shared board stayed apart
for good after the second one's upgrade.

A try declared lost, or dropped with the epoch's flights, now lets the
next packet try again. test-link's refused_restarted case: the receiver
refuses a stream, is killed while the next try is due and comes back 8
s later with the input; before, nothing was stored in 120 s, now all
200 are by 18.2 s. Streams refused for good send as few packets as
before (9 in 90 s).

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