Switch to using port 80 by default, and (by necessity) add a drop-privs mode.

Connecting to the database has to be deferred until privs have been dropped.
This probably breaks non-__main__ usage, but I'm not sure that wasn't already
broken. If/when it's ever needed, check it thoroughly.
Merge pull request #119 from Rosuav/port_80

Switch to using port 80 by default, and (by necessity) add a drop-privs mode.