Core/Maps:

* Scarlet Monastry will now properly scale down to normal difficulty when trying to enter the instance on heroic difficulty
* removed deprecated quest text requirement from access_requirement
* added new access_requirement field to specifiy if a dungeon is only available for heroic difficulty
* added heroic exclusive access_requirement entries for Zul'Gurub, Zul'Aman, End Time, Well of Eternity and Hour of Twilight
* Players will no longer be able to enter dungeons when a encounter is in progress

src/server/game/Maps/Map.cpp

@@ -3841,7 +3841,7 @@ Map::EnterState InstanceMap::CannotEnter(Player* player)
     }
 
     // cannot enter while an encounter is in progress (unless this is a relog, in which case it is permitted)
-    if (!player->IsLoading() && IsRaid() && GetInstanceScript() && GetInstanceScript()->IsEncounterInProgress())
+    if (!player->IsLoading() && (IsDungeon() || IsRaid()) && GetInstanceScript() && GetInstanceScript()->IsEncounterInProgress())
         return CANNOT_ENTER_ZONE_IN_COMBAT;
 
     // cannot enter if player is permanent saved to a different instance id