Fix expansion of the $parentclassname special variable

It incorrectly contains brackets in the expanded name.
Fixes SF Bug 1375.

Examples/test-suite/extend_special_variables.i

@@ -19,3 +19,16 @@
 struct ForExtension {
 };
 %}
+
+%inline %{
+namespace Space {
+  template <class T> class ExtendTemplate {};
+}
+%}
+
+%extend Space::ExtendTemplate
+{
+   void extending() { $parentclassname tmp; }
+}
+
+%template(ExtendTemplateInt) Space::ExtendTemplate<int>;