sync: signatures sent again after a failed send

A sync message whose send fails gives back the changes it carried: the
next message takes them again. The signatures it carried weren't
given back: the peer's cursor stayed past them, so the changes went
again without them, and under a policy requiring signatures waited
for them until the next session; SIGNATURES no longer covers that.
A failed send now sends the peer all signatures again with the next
changes (each actor's latest, a few hundred at most).

0 files changed, 0 insertions, 0 deletions