Revert "PL/Python: Remove workaround for returning booleans in Python <2.3"

This reverts commit be0dfbad.

The previous information that Py_RETURN_TRUE and Py_RETURN_FALSE are
supported in Python 2.3 is wrong.  They require Python 2.4.  Update the
comment about that.

src/pl/plpython/plpy_typeio.c

@@ -492,9 +492,15 @@ PLy_input_datum_func2(PLyDatumToOb *arg, Oid typeOid, HeapTuple typeTup)
 static PyObject *
 PLyBool_FromBool(PLyDatumToOb *arg, Datum d)
 {
+	/*
+	 * We would like to use Py_RETURN_TRUE and Py_RETURN_FALSE here for
+	 * generating SQL from trigger functions, but those are only supported in
+	 * Python >= 2.4, and we support older versions.
+	 * http://docs.python.org/api/boolObjects.html
+	 */
 	if (DatumGetBool(d))
-		Py_RETURN_TRUE;
-	Py_RETURN_FALSE;
+		return PyBool_FromLong(1);
+	return PyBool_FromLong(0);
 }
 
 static PyObject *