clear -classes and support. * ov-class.h (octave_class::clear_exemplar_map): New function. * ov-class.cc (octave_class::clear_exemplar_map): New function. * symtab.h (symbol_record::clear_objects): New function * symtab.h (symbol_record::do_clear_objects): New function * variables.cc (do_matlab_compatible_clear, clear): Added classes option