#384 Grouped mob loot

Grouped mobs should only drop chests after the entire encounter has been defeated.

-- this may only pertain to named mobs need to do more research

Adding a new column to the spawn table:

alter table spawn add column loot_drop_type int(10) unsigned not null default 0;

• loot_drop_type of 0 means spawn will when part of an encounter transfer its loot to the next alive spawn.
• loot_drop_type of 1 means the spawn will drop its own loot when it dies (like a named mob ideally).
• These changes do not change body drops which remain on the spawn/npc that dies, not transferred.
• loot and chest drops have been expanded beyond NPC's which means potential PVP support or even other types of spawns can drop loot/chests (probably expand loot_drop_type at a later time for more options in this area). Need lua interface support (when player dies and all that) issue #436 opened for it.
• some additional mutex lock protections on spawn loot
• SetLootTier(loot_tier) and GetLootTier(), SetLootDropType(drop_type) and GetLootDropType() added to lua