Use GUIDs instead of "global" pointers in ~all boss/instance scripts.

GUIDs are most safer than pointers and in some cases can avoid segmentation faults.

== - ==

Let me show a simple example:

We have a pointer to a creature: Creature *pCreature;

and try to search a creature and store it in the pointer:
pCreature = SearchCreature(ID);

We can check simply if the creature found or not:
if(pCreature)
- if this give true: creature found and we have a memory address which points to the creature
- if this give false: creature not found and this is a NULL pointer

Suppose that we have a valid pointer, so creature found.
We wanna use that pointer somewhere, for example in script phase 3.
But we delete the creature(from world) in phase 1.
In phase 3:
if(pCreature)
    pCreature->DoSomeShit();
The if condition gives true, but pCreature points to an _invalid_ address.
In that address maybe have "nothing" or another creature's object or a player or anything else, dont know that.

~~ - ~~

Let me show the correct way:
Creature's GUID: uint64 CreatureGUID;

search the creature and set the GUID:
Creature *pCreature = SearchCreature(ID);
CreatureGUID = pCreature ? pCreature->GetGUID() : 0; // if pCreature is NULL set the GUID to 0

So we have a GUID and not a pointer.
We can get the creature from that GUID:
Creature *pCreature = GetCreature(CreatureGUID);
and we can simply check it is valid or not(found or not):
if(pCreature)

So we deleted the creature in phase 1 and try to use it in phase 3:
Creature *pCreature = GetCreature(CreatureGUID);
And this gives NULL because GetCreature() can't find the creature which GUID is CreatureGUID.

if(pCreature) // pCreature is NULL
    pCreature->DoSomeShit(); // DoSomeShit() not called

== - ==

Remove some not used variables.
Some clean.

TODO: Should search/fix these in zones scripts.

--HG--
branch : trunk

src/scripts/northrend/utgarde_keep/utgarde_pinnacle/boss_svala.cpp

@@ -89,6 +89,7 @@ struct boss_svalaAI : public ScriptedAI
     IntroPhase Phase;
 
     TempSummon* pArthas;
+    uint64 ArthasGUID;
 
     ScriptedInstance* pInstance;
 
@@ -97,7 +98,7 @@ struct boss_svalaAI : public ScriptedAI
         Phase = IDLE;
         uiIntroTimer = 1000;
         uiIntroPhase = 0;
-        pArthas = NULL;
+        ArthasGUID = 0;
 
         if (pInstance)
             pInstance->SetData(DATA_SVALA_SORROWGRAVE_EVENT, NOT_STARTED);
@@ -113,10 +114,11 @@ struct boss_svalaAI : public ScriptedAI
             Phase = INTRO;
             m_creature->SetFlag(UNIT_FIELD_FLAGS, UNIT_FLAG_NON_ATTACKABLE);
 
-            if (pArthas = m_creature->SummonCreature(CREATURE_ARTHAS, 295.81, -366.16, 92.57, 1.58, TEMPSUMMON_MANUAL_DESPAWN))
+            if (Creature *pArthas = m_creature->SummonCreature(CREATURE_ARTHAS, 295.81, -366.16, 92.57, 1.58, TEMPSUMMON_MANUAL_DESPAWN))
             {
                 pArthas->SetFlag(UNIT_FIELD_FLAGS, UNIT_FLAG_NON_ATTACKABLE|UNIT_FLAG_NOT_SELECTABLE);
                 pArthas->SetFloatValue(OBJECT_FIELD_SCALE_X, 5);
+                ArthasGUID = pArthas->GetGUID();
             }
         }
     }
@@ -130,6 +132,7 @@ struct boss_svalaAI : public ScriptedAI
 
         if (uiIntroTimer <= diff)
         {
+            Creature *pArthas = Unit::GetCreature(*m_creature, ArthasGUID);
             if (!pArthas)
                 return;
 
@@ -171,8 +174,8 @@ struct boss_svalaAI : public ScriptedAI
                     {
                         m_creature->SetFlag(UNIT_FIELD_FLAGS, UNIT_FLAG_NON_ATTACKABLE|UNIT_FLAG_NOT_SELECTABLE);
                         m_creature->SetDisplayId(DATA_SVALA_DISPLAY_ID);
-                        pArthas->UnSummon();
-                        pArthas = NULL;
+                        ((TempSummon*)pArthas)->UnSummon(); // TODO: should need a ToTempSummon()
+                        ArthasGUID = 0;
                         Phase = FINISHED;
                     }
                     else