Bukkit

Added PvP limits. Freshly joined and freshly respawned players can't participate in PvP until they pick up an item (should reduce camping).

Can disable PvP altogether. World-based PvP toggle will come later.

Note that poison splash potion still works (even versus "pvp immune" players), but isn't fatal. I'm looking for ways to fix that. Other spash potions are correctly blocked.

Also fixed a bug you may have noticed in your logs about blocks spreading.