Fix READLINE blinking with bind -x

[tinmarino]

See in code why it happens and find a trick (like double buffering or cheaty redirection) to prevent user command line to disapear and appear again (alias flinkering)

[tinmarino]

From bashline.c::bash_execute_unix_command

  ce = rl_get_termcap ("ce");
  if (ce)	/* clear current line */
    {
      rl_clear_visible_line ();
      fflush (rl_outstream);
    }
  else
    rl_crlf ();	/* move to a new line */

# ....
  v = find_variable ("READLINE_LINE");
  maybe_make_readline_line (v ? value_cell (v) : 0);

# ...
  /* and restore the readline buffer and display after command execution. */
  /* If we clear the last line of the prompt above, redraw only that last
     line.  If the command returns 124, we redraw unconditionally as in
     previous versions. */
  if (ce && r != 124)
    rl_redraw_prompt_last_line ();
  else
    rl_forced_update_display ();