Added new type-safe cast functions.

This, when properly used, should get rid of most memory corruption issues,
currently, casting types C-style with no checks leads to some abstract crashing.
Functionality is same as with dynamic_cast<>, but with no RTTI check - so when
casting into invalid type you will receive NULL, and most probably crash.
At the same time, i took the liberty to convert most Player* casts to ToPlayer().
Still needs crapload of casts being moved to new facility.

--HG--
branch : trunk

src/game/QuestHandler.cpp

@@ -125,7 +125,7 @@ void WorldSession::HandleQuestgiverAcceptQuestOpcode( WorldPacket & recv_data )
     // no or incorrect quest giver
     if(!pObject
         || (pObject->GetTypeId() != TYPEID_PLAYER && !pObject->hasQuest(quest))
-        || (pObject->GetTypeId() == TYPEID_PLAYER && !((Player*)pObject)->CanShareQuest(quest))
+        || (pObject->GetTypeId() == TYPEID_PLAYER && !pObject->ToPlayer()->CanShareQuest(quest))
         )
     {
         _player->PlayerTalkClass->CloseGossip();