Andrew's hint has allowed me to progress.  Changing
permissions on /var/tmp/vi.recover helped.  But, now
I see:

% vi foobar
ex/vi: Error: Log file: No such file or directory

The man page doesn't tell me where it's trying to
make the log file, and using strings etc. doesn't
seem to give me any hints.  I'm still downloading
the source so I can't check that either.

Dave