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/SpellHandler.cpp

@@ -314,7 +314,7 @@ void WorldSession::HandleCastSpellOpcode(WorldPacket& recvPacket)
     if(mover->GetTypeId() == TYPEID_PLAYER)
     {
         // not have spell in spellbook or spell passive and not casted by client
-        if (!((Player*)mover)->HasActiveSpell (spellId) || IsPassiveSpell(spellId) )
+        if (!mover->ToPlayer()->HasActiveSpell (spellId) || IsPassiveSpell(spellId) )
         {
             //cheater? kick? ban?
             recvPacket.rpos(recvPacket.wpos());                 // prevent spam at ignore packet