Persistence: Test cases for content dump

It turned our that the document could not be dumped as the xml specifier was used as first element. As the dumping added the <content> element around it was invalid. However, content is required to read properties. Hence the xml element generation was moved.

src/App/PropertyContainerPyImp.cpp

@@ -231,7 +231,7 @@ PyObject* PropertyContainerPy::dumpPropertyContent(PyObject *args, PyObject *kwd
  
     int compression = 3;
     char* property;
-    static char* kwds_def[] = {"Compression",NULL};
+    static char* kwds_def[] = {"Property", "Compression",NULL};
     PyErr_Clear();
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "s|i", kwds_def, &property, &compression)) {
         return NULL;