Remove stuff made obsolete by making players more ActiveObject-like and raise protocol version number by one (because it is not compatible at all anymore)

Fix processing of the default_password setting. It is now actually used as the plaintext password for new users. Also add /setpassword and /clearpassword server commands that can be used by admins with the PRIV_PASSWORD privilege, and update the /help message.

Make map generator as much threaded as possible (not much benefit with current generator because of small generator chunk size (a single MapBlock))