3351: Set PUT request timeout to 60 seconds.
3351: Do not use resume cache at all if --no-resume flag is given.
3351: Improve "already uploading" message (and send to stderr, not stdout).
3351: Retry failed threads (servers) if replication is too low after one pass.
3351: Catch SSLError and show warning instead of stack trace.
3351: Clean up some excess indentation.
3351: Add comment about SSL timeouts.
3351: Fix CollectionReader usage in arv-ls.
3351: Propagate caller-provided timeout from KeepClient to KeepWriterThread.

Also, use the timeout in the sign_for_old_server block (even though
this branch is unlikely to be used in real life now that the old Keep
server has been replaced).
Merge branch '3351-keep-timeout' closes #3351