[PATCH] Fix -W* documentation, update to contrib/check_warning_flags.sh

[FX Coudert]

> gcc/fortran/ChangeLog:
> 2008-02-20  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
>
> 	* invoke.texi (Error and Warning Options): Document
> 	-Wline-truncation.

That part is OK.

FX