Allow to call superclass constructor without arguments. * ov-classdef.cc (octave_classdef_superclass_ref::function_value): New method. * pt-funcall.h (tree_funcall::rvalue): Move definition to C++. * pt-funcall.cc (tree_funcall::rvalue): Moved from header. If the result of the function call is a single function object, re-index the function to yield the proper result it required (similar logic as in pt-id.cc).

--- a/libinterp/octave-value/ov-classdef.cc
+++ b/libinterp/octave-value/ov-classdef.cc
@@ -1040,6 +1040,8 @@
 
   ~octave_classdef_superclass_ref (void) { }
 
+  octave_function* function_value (bool = false) { return this; }
+
   octave_value_list
   subsref (const std::string& type,
            const std::list<octave_value_list>& idx,