Revert ServerAliveInterval change in 6.20161111, which caused problems
with too many old versions of ssh and unusual ssh configurations.
It should have not been needed anyway since ssh is supposted to
have TCPKeepAlive enabled by default.
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.
