Support rsync daemon over SSL via stunnel.

Added the client rsync-ssl script and various client/daemon support
files needed for talking to an rsync daemon over SSL on port 874 (no
tls support).  This uses an elegant stunnel setup that was detailed
by dozzie (see the resources page) now that stunnel4 has improved
command-spawning support.  Also incorporates some tweaks by devzero
(e.g. the nice no-tmpfile-config client-side code) and a few by me
(including logging of the actual remote IP that came in to the
stunnel process).  This probably still needs a little work.