further improvements

dialogs/mediapropertiesdialog.cpp

@@ -185,7 +185,7 @@ void MediaPropertiesDialog::accept() {
 	}
 	ca->appendPost(new UpdateViewer());
 
-	undo_stack.push(ca);
+	Olive::UndoStack.push(ca);
 
 	QDialog::accept();
 }

dialogs/newsequencedialog.cpp

@@ -76,7 +76,7 @@ void NewSequenceDialog::create() {
 
 		ComboAction* ca = new ComboAction();
 		panel_project->new_sequence(ca, s, true, nullptr);
-		undo_stack.push(ca);
+		Olive::UndoStack.push(ca);
 	} else {
 		ComboAction* ca = new ComboAction();
 
@@ -98,7 +98,7 @@ void NewSequenceDialog::create() {
 			}
 		}
 
-		undo_stack.push(ca);
+		Olive::UndoStack.push(ca);
 	}
 
 	accept();

dialogs/replaceclipmediadialog.cpp

@@ -101,7 +101,7 @@ void ReplaceClipMediaDialog::replace() {
 					}
 				}
 
-				undo_stack.push(rcmc);
+				Olive::UndoStack.push(rcmc);
 
 				close();
 			}

dialogs/speeddialog.cpp

@@ -405,7 +405,7 @@ void SpeedDialog::accept() {
 	sel_command->new_data = Olive::ActiveSequence->selections;
 	ca->append(sel_command);
 
-	undo_stack.push(ca);
+    Olive::UndoStack.push(ca);
 
 	update_ui(true);
 	QDialog::accept();