(svn r27272) [1.5] -Backport from trunk:

- Fix: ScriptList::RemoveList failed to remove a list from itself [FS#6287] (r27258)
- Fix: Combined button+dropdown widgets in order and autoreplace GUI had incorrect hitbox when using GUI zoom [FS#6270] (r27255)
- Fix: When building a lock on DC_AUTO-removable water-based objects, the water class was always set to canal [FS#6264] (r27254)
- Fix: When crossing tram tracks with railroads, cost of extra roads was not being counted [FS#6282] (r27253)

src/script/api/script_list.cpp

@@ -556,6 +556,8 @@ void ScriptList::Sort(SorterType sorter, bool ascending)
 
 void ScriptList::AddList(ScriptList *list)
 {
+	if (list == this) return;
+
 	ScriptListMap *list_items = &list->items;
 	for (ScriptListMap::iterator iter = list_items->begin(); iter != list_items->end(); iter++) {
 		this->AddItem((*iter).first);
@@ -565,6 +567,8 @@ void ScriptList::AddList(ScriptList *list)
 
 void ScriptList::SwapList(ScriptList *list)
 {
+	if (list == this) return;
+
 	this->items.swap(list->items);
 	this->buckets.swap(list->buckets);
 	Swap(this->sorter, list->sorter);
@@ -694,9 +698,13 @@ void ScriptList::RemoveList(ScriptList *list)
 {
 	this->modifications++;
 
-	ScriptListMap *list_items = &list->items;
-	for (ScriptListMap::iterator iter = list_items->begin(); iter != list_items->end(); iter++) {
-		this->RemoveItem((*iter).first);
+	if (list == this) {
+		Clear();
+	} else {
+		ScriptListMap *list_items = &list->items;
+		for (ScriptListMap::iterator iter = list_items->begin(); iter != list_items->end(); iter++) {
+			this->RemoveItem((*iter).first);
+		}
 	}
 }
 
@@ -756,14 +764,12 @@ void ScriptList::KeepBottom(int32 count)
 
 void ScriptList::KeepList(ScriptList *list)
 {
+	if (list == this) return;
+
 	this->modifications++;
 
 	ScriptList tmp;
-	for (ScriptListMap::iterator iter = this->items.begin(); iter != this->items.end(); iter++) {
-		tmp.AddItem((*iter).first);
-		tmp.SetValue((*iter).first, (*iter).second);
-	}
-
+	tmp.AddList(this);
 	tmp.RemoveList(list);
 	this->RemoveList(&tmp);
 }