[svn] Enable linked spells: cast spells/remove auras when spells casted/spells hitting/auras removed. Add new table "spell_linked_spell". Some illustrations provided in sql.

Let trigger creature cast AOE spells when summoned. Illustration provided in sql.
Let active creatures always visible if possible. (seems does not work for now, need to find out why)

--HG--
branch : trunk

src/game/World.cpp

@@ -1096,6 +1096,9 @@ void World::SetInitialWorldSettings()
     sLog.outString( "Loading spell extra attributes...(TODO)" );
     spellmgr.LoadSpellExtraAttr();
 
+    sLog.outString( "Loading linked spells..." );
+    spellmgr.LoadSpellLinked();
+
     sLog.outString( "Loading player Create Info & Level Stats..." );
     objmgr.LoadPlayerInfo();