use TopologicalOrder for evaluating moves

The dag package did not previously provide a topological walk of a given
graph. While the existing combination of a transitive reduction with a
depth-first walk appeared to accomplish this, depth-first is only
equivalent with a simple tree. If there are multiple paths to a node, a
depth-first approach will skip dependencies from alternate paths.

internal/refactoring/move_execute.go

@@ -92,7 +92,7 @@ func ApplyMoves(stmts []MoveStatement, state *states.State) MoveResults {
 		}
 	}
 
-	g.ReverseDepthFirstWalk(startNodes, func(v dag.Vertex, depth int) error {
+	for _, v := range g.ReverseTopologicalOrder() {
 		stmt := v.(*MoveStatement)
 
 		for _, ms := range state.Modules {
@@ -187,9 +187,7 @@ func ApplyMoves(stmts []MoveStatement, state *states.State) MoveResults {
 				panic(fmt.Sprintf("unhandled move object kind %s", kind))
 			}
 		}
-
-		return nil
-	})
+	}
 
 	return ret
 }