[12415] Avoid creature not respawning when not looted.

This occurs when corpse decay time is bigger than respawn time.
This is not blizzlike, to permit a creature respawn when its corpse still exist we need a complete rewrite of creature pool system.

Fix cmangos/mangos-wotlk#72
Merge pull request #3 from cmangos/master

Sync with cmangos/mangos-wotlk