Fix HandleStatModifier for BASE_PCT and TOTAL_PCT modifierType.

Formula was incorrect. It gave a slight advantage when there are several auras for the same UnitMod.
Ex: if you had 2 auras giving 50%,
- previous formula would give: 1*1.5*1.5=2.25
- new formula give: 1+0.5+0.5=2.00 which is correct.

Hack for negative pct <= -100 is also no longer necessary

--HG--
branch : trunk

src/game/Unit.cpp

@@ -12621,8 +12621,6 @@ bool Unit::HandleStatModifier(UnitMods unitMod, UnitModifierType modifierType, f
         return false;
     }
 
-    float val = 1.0f;
-
     switch (modifierType)
     {
         case BASE_VALUE:
@@ -12631,14 +12629,7 @@ bool Unit::HandleStatModifier(UnitMods unitMod, UnitModifierType modifierType, f
             break;
         case BASE_PCT:
         case TOTAL_PCT:
-            if (amount <= -100.0f)                           //small hack-fix for -100% modifiers
-                amount = -200.0f;
-
-            val = (100.0f + amount) / 100.0f;
-            m_auraModifiersGroup[unitMod][modifierType] *= apply ? val : (1.0f/val);
-            break;
-
-        default:
+            m_auraModifiersGroup[unitMod][modifierType] += (apply ? amount : -amount) / 100.0f;
             break;
     }