localize use of yylval.tok_val in lexical_feedback member functions * lex.h, lex.ll (lexical_feedback::push_token): New function. (lexical_feedback::current_token): New function. (lexical_feedback::token_stack): Now private. * lex.ll (TOK_PUSH_AND_RETURN, BIN_OP_RETURN_INTERNAL, lexical_feedback::is_keyword_token, lexical_feedback::handle_number, lexical_feedback::handle_string, lexical_feedback::handle_superclass_identifier, lexical_feedback::handle_meta_identifier, lexical_feedback::handle_identifier, lexical_feedback::display_token): Use push_token and current_token instead of accessing yylval.tok_val directly.