Python builtin - add indexing support to std::unordered_set

Examples/test-suite/python/cpp11_hash_tables_runme.py

@@ -38,6 +38,7 @@ for x in [cpp11_hash_tables.SetInt([1]),
 		  cpp11_hash_tables.UnorderedMultiSetInt([1])]:
 
 	swig_assert_equal([e for e in x], [1])
+	swig_assert_equal(x[0], 1)
 
 	swig_assert_equal(1 in x, True)
 	swig_assert_equal(2 in x, False)

Lib/python/std_unordered_set.i

@@ -45,8 +45,10 @@
 
 #if defined(SWIGPYTHON_BUILTIN)
   %feature("python:slot", "sq_contains", functype="objobjproc") __contains__;
+  %feature("python:slot", "mp_subscript", functype="binaryfunc") __getitem__;
 #endif
 
+
   %extend  {
      void append(value_type x) {
        self->insert(x);