Implement "isa" for classdef objects. * ov.h (octave_value::is_instance_of): New method. * ov-base.h (octave_base_value::is_instance_of): Likewise. * ov-class.h (octave_class::is_instance_of): New method declaration. * ov-class.cc (octave_class::is_instance_of): Implement it with find_parent_class. * ov-classdef.h (octave_classdef::is_instance_of): New method declaration. * ov-classdef.cc (octave_classdef::is_instance_of): Implement it with lookup_class and is_superclass.

((nil .
      ((c-file-style . "gnu")
       (indent-tabs-mode . nil)
       (fill-column . 72)
       (eval . (when (and (buffer-file-name)
                          (string-match-p "\\.h\\'" (buffer-file-name))
                          (not (string-match-p "/gnulib/" (buffer-file-name))))
                 (c++-mode)
                 (c-set-style "gnu")))))
 (change-log-mode . ((indent-tabs-mode . t)))
 (makefile-mode . ((indent-tabs-mode . t))))