tap: some preparatory refactoring (1) This refactoring is aimed at simplifying the introduction of colored console output for the TAP driver. * lib/tap-driver (console_output): Now accept two arguments, the first one indicating which kind of thing is to be displayed (for now only a test result or a diagnostic comment), and the second one (if present) the message associated to it. (handle_tap_test, handle_tap_comment, handle_tap_plan, testsuite_error): Adapt to the new `console_output' interface.