[Fortran, Patch] Improve documentation of the non-implemented RECORD STRUCTURE extension

[Tobias Burnus]

*ping*

Tobias Burnus:
> During the discussion of UNION, I decided to have a look at the 
> current documentation. UNION is not mentioned (except for some 
> commented lines), but record structures are. Attached is an attempted 
> to improve the documentation.
>
> The current version is at 
> http://gcc.gnu.org/onlinedocs/gfortran/STRUCTURE-and-RECORD.html
>
> I tested it with make pdf and make info and looked at the output.
> OK for the trunk?
>
> Tobias