Make a function(ToTempSummon()) which can convert Creature to TempSummon with a C++ cast(reinterpret_cast) and with a type check(isSummon()).

This function is like ToPlayer(), ToTotem(), etc.

This commit is like ede831bdd6f0cff481acc33f269fa7f8c78befd4 / r7496:
http://code.google.com/p/trinitycore/source/detail?r=ede831bdd6f0cff481acc33f269fa7f8c78befd4
As a result, this commit has the advantages and the "disadvantages" too, like r7496.

Please try to be polite if this commit causes some crashes.

--HG--
branch : trunk

src/game/TemporarySummon.cpp

@@ -197,7 +197,7 @@ void TempSummon::InitStats(uint32 duration)
             {
                 Creature *oldSummon = GetMap()->GetCreature(owner->m_SummonSlot[slot]);
                 if(oldSummon && oldSummon->isSummon())
-                    ((TempSummon*)oldSummon)->UnSummon();
+                    oldSummon->ToTempSummon()->UnSummon();
             }
             owner->m_SummonSlot[slot] = GetGUID();
         }