So that stalled transfers will be noticed within about 3 minutes,
even if TCPKeepAlive is disabled or doesn't work.
Rather than setting with -o, use -F with another config file,
so that any settings in ~/.ssh/config or /etc/ssh/ssh_config overrides this.
If a transfer fails for some reason, but some data managed to be sent, the
transfer will be retried. (The assistant already did this.)
Possible impacts:
* More ssh prompts if ssh needs to prompt for a password to connect to a
host, or is prompting about some other problem like a ssh key mismatch.
* More data transfer due to retrying, epecially when a remote does not
support resuming a transfer.
In the worst case, a lot of data will be transferred but it fails before
the end, and then all that data gets transferred again plus one byte more;
repeat until it manages to get the whole file.
