bug#744: nroff-mode auto-fill-mode not on directives

[Werner LEMBERG]

> I've been using the regexp below, which suppresses auto-fill on .IP
> and the like, but continues to auto-fill the comment directives (no
> change)
> 
>     .\"    traditional
>     .\#    groff extension

The real groff extension is that `\#' at the beginning of a line
completely removes it:

  This is a
  \# comment
  test.

    -> This is a test.

Auto-fill would be possible for .IP and friends too, provided you end
the line with `\'.

  .IP This is a long title \
  continued on the next line.


      Werner