deprecate symbol_table::varref functions * ov-usr-fcn.h (octave_user_function::argn_varref, octave_user_function::nargin_varref, octave_user_function::nargout_varref, octave_user_function::varargin_varref): Delete unused variables. * symtab.h (symbol_table::symbol_record::symbol_record_ref::assign, symbol_table::symbol_record::symbol_record_ref::do_non_const_unary_op, symbol_table::symbol_record::do_non_const_unary_op, (symbol_table::symbol_record::is_undefined, symbol_table::symbol_record::assign, symbol_table::assign, symbol_table::force_assign, symbol_table::global_assign, symbol_table::persistent_assign, symbol_table::top_level_assign, symbol_table::do_assign, symbol_table::do_persistent_assign): New functions. (symbol_table::symbol_record::symbol_record_ref::varref): Avoid calls to deprecated functions. (symbol_table::varref, symbol_table::force_varref, symbol_table::global_varref, symbol_table::persistent_varref, symbol_table::top_level_varref, symbol_table::do_varref, symbol_table::do_persistent_varref): Deprecate. (symbol_table::symbol_reference::is_black_hole): New function. * oct-lvalue.h, oct-lvalue.cc: Store symbol_reference instead of pointer to octave_value object. (octave_lvalue::value): Now const. (octave_lvalue::object): Delete. * pt-id.cc (tree_identifier::lvalue): Construct octave_lvalue from sym, not sym->varref. * ls-mat5.cc, oct-lvalue.cc, oct-lvalue.h, pt-jit.cc, error.cc, load-save.cc, symtab.cc, symtab.h, variables.cc, ov-fcn-handle.cc, ov-usr-fcn.cc, ov-usr-fcn.h, oct-parse.in.yy, pt-eval.cc, pt-id.h, pt-idx.cc, mex.cc: Change all uses of varref functions to use assign instead. Use varval instead of varref where appropriate. * load-save.cc (install_loaded_variable): Don't manipulate symbol_record directly.