Core: optimize string splitting

- Mainly affects item loading performance
  - Reduces guild loading time a lot

--HG--
branch : trunk

src/server/game/Instances/InstanceSaveMgr.cpp

@@ -219,7 +219,7 @@ bool InstanceSave::UnloadIfEmpty()
 
 void InstanceSaveManager::_DelHelper(const char *fields, const char *table, const char *queryTail,...)
 {
-    Tokens fieldTokens = StrSplit(fields, ", ");
+    Tokens fieldTokens(fields, ',');
     ASSERT(fieldTokens.size() != 0);
 
     va_list ap;