Correct notes on customising Python builtin comparison operators

Also add example for python:compare feature

Examples/test-suite/python/python_builtin_runme.py

@@ -45,3 +45,26 @@ if is_python_builtin():
   del d
   if cvar.Dealloc3CalledCount != 1:
     raise RuntimeError("count should be 1")
+
+  # Test 5 for python:compare feature
+  m10 = MyClass(10)
+  m20 = MyClass(20)
+  m15 = MyClass(15)
+
+  if not m10 < m15:
+    raise RuntimeError("m10 < m15")
+  if not m10 < m20:
+    raise RuntimeError("m10 < m20")
+  if not m15 < m20:
+    raise RuntimeError("m15 < m20")
+
+  if m10 > m15:
+    raise RuntimeError("m10 > m15")
+  if m10 > m20:
+    raise RuntimeError("m10 > m20")
+  if m15 > m20:
+    raise RuntimeError("m15 > m20")
+
+  if MyClass.less_than_counts != 6:
+    raise RuntimeError("python:compare feature not working")
+

Examples/test-suite/python_builtin.i

@@ -112,3 +112,19 @@ void Dealloc2Destroyer(PyObject *v) {
 }
 %}
 
+// Test 5 for python:compare feature
+%feature("python:compare", "Py_LT") MyClass::lessThan;
+
+%inline %{
+  class MyClass {
+  public:
+    MyClass(int val = 0) : val(val) {}
+    bool lessThan(const MyClass& other) const {
+      less_than_counts++;
+      return val < other.val;
+    }
+    int val;
+    static int less_than_counts;
+  };
+  int MyClass::less_than_counts = 0;
+%}