gsoc08-privileges branch merged

[Joshua Root]

I just finished merging the changes from the gsoc08-privileges branch
back into trunk. This of course has the potential for breakage, though I
changed the default back to running as root, so you should hopefully not
see any problems unless you pass --with-macports-user=you to configure.

The privilege dropping has its issues. For example, if you start port
with sudo, the configure and build phases will be run as root. But then
root privileges will be dropped by the time it tries to clean after
installing, with predictable results.

So there's still some tweaking to be done, but I figured the sooner it
was merged, the less bitrot there'd be to deal with.

- Josh