Security audit

Don't produce stack trace which looks like crash/include file name in
logging stats

Add to above Dean Gaudet's suggestion: make errors look prettier (like tar).

Examine certain network settings like Globals.conn_bufsize and whether
or not ssh is used with compression, and find good defaults or add
easy to use switches.

Examine and fix recovery problems.

Add options to pass to ssh (e.g. compression, maybe arbitrary options).

Think about adding Gaudet's idea for keeping track of renamed files.

--read-only and --write-only /usr/foo switches to tighten security up some.