Fix python default_args testcase for Python 3

Changes for the default_args testcase to run under Python 3 when called
from python_default_args testcase

Examples/test-suite/python_default_args.i

@@ -3,6 +3,7 @@
 %pythondefaultargs;
 
 // Turn off the feature for the tricky cases that can't be handled
+%nopythondefaultargs trickyvalue3; // 'mode=0644' is okay in Python 2, but no Python 3
 %nopythondefaultargs seek;
 %nopythondefaultargs Space::Klass::inc;
 %nopythondefaultargs DerivedEnumClass::accelerate;