+ use undo/redo for Fem constraint force dialog

src/Mod/Fem/Gui/TaskFemConstraintForce.cpp

@@ -329,6 +329,15 @@ TaskDlgFemConstraintForce::TaskDlgFemConstraintForce(ViewProviderFemConstraintFo
 
 //==== calls from the TaskView ===============================================================
 
+void TaskDlgFemConstraintForce::open()
+{
+    // a transaction is already open at creation time of the panel
+    if (!Gui::Command::hasPendingCommand()) {
+        QString msg = QObject::tr("Constraint force");
+        Gui::Command::openCommand((const char*)msg.toUtf8());
+    }
+}
+
 bool TaskDlgFemConstraintForce::accept()
 {
     std::string name = ConstraintView->getObject()->getNameInDocument();
@@ -360,4 +369,14 @@ bool TaskDlgFemConstraintForce::accept()
     return TaskDlgFemConstraint::accept();
 }
 
+bool TaskDlgFemConstraintForce::reject()
+{
+    // roll back the changes
+    Gui::Command::abortCommand();
+    Gui::Command::doCommand(Gui::Command::Gui,"Gui.activeDocument().resetEdit()");
+    Gui::Command::updateActive();
+
+    return true;
+}
+
 #include "moc_TaskFemConstraintForce.cpp"