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).