I'd like some feedback on ftp -k `in the field'.

If you followed the commit, you know that ftp in -current can,
as an option, send `extra' commands to make sure the control
connection stays alive.

I wrote this because of some specific setup at work, and it helps
me a great deal.

However, I have no idea:
- how current this kind of situation might be.
- if the -k option is kosher with all ftp servers.

So, if you had flaky ftp, and the new option helps, or if you tried
the new option, and find out some ftp servers/proxys that don't like it,
I'd be happy to know.