don't resend sync messages to up-to-date peers

When an sync messages arrives and automerge has nothing to say about it,
then no reply is generated.  With c9279e4 it was assumed that every sync
message gets an answer, so missing replies caused unnecessary resends.

Now a reply is only awaited if the peer's last reported heads differ
from ours. If the peer's heads become equal through a third peer without
replying, the waiting will also abort if a ping or pong showss the same
heads digest on both sides.

0 files changed, 0 insertions, 0 deletions