Make PartDesign::Boolean work with new Link structure

This is the first feature that used GeoFeatureGroupExtension and required links to the groups inside as well as to things on the same level. Hence a few modifications to link scopes have been nesseccary.

src/App/GroupExtensionPyImp.cpp

@@ -131,6 +131,44 @@ PyObject* GroupExtensionPy::addObjects(PyObject *args) {
     throw Base::TypeError(error);
 };
 
+
+PyObject* GroupExtensionPy::setObjects(PyObject *args) {
+    
+    PyObject *object;
+    if (!PyArg_ParseTuple(args, "O", &object))     // convert args: Python->C
+        return NULL;                             // NULL triggers exception
+        
+    if (PyTuple_Check(object) || PyList_Check(object)) {
+        Py::Sequence list(object);
+        Py::Sequence::size_type size = list.size();
+        std::vector<DocumentObject*> values;
+        values.resize(size);
+
+        for (Py::Sequence::size_type i = 0; i < size; i++) {
+            Py::Object item = list[i];
+            if (!PyObject_TypeCheck(*item, &(DocumentObjectPy::Type))) {
+                std::string error = std::string("type in list must be 'DocumentObject', not ");
+                error += (*item)->ob_type->tp_name;
+                throw Base::TypeError(error);
+            }
+
+            values[i] = static_cast<DocumentObjectPy*>(*item)->getDocumentObjectPtr();
+        }
+
+        GroupExtension* grp = getGroupExtensionPtr();
+        auto vec = grp->setObjects(values); 
+        Py::List result;
+        for (App::DocumentObject* obj : vec)
+            result.append(Py::asObject(obj->getPyObject()));
+
+        return Py::new_reference_to(result);
+    }
+    
+    std::string error = std::string("type must be list of 'DocumentObject', not ");
+    error += object->ob_type->tp_name;
+    throw Base::TypeError(error);
+};
+
 PyObject*  GroupExtensionPy::removeObject(PyObject *args)
 {
     PyObject *object;