[gfortran] Add new -std=legacy command line option

[Paul Brook]

> 2005-05-28  Roger Sayle  <roger@eyesopen.com>
>
> 	* gfortran.h (GFC_STD_LEGACY): New "standard" macro.  Reindent.
> 	* options.c (gfc_init_options): By default, allow legacy extensions
> 	but warn about them.
> 	(gfc_post_options): Make -pedantic warn about legacy extensions
> 	even with -std=legacy.
> 	(gfc_handle_option): Make -std=gnu follow the default behaviour
> 	of warning about legacy extensions, but allowing them. Make the
> 	new -std=legacy accept everything and warn about nothing.
> 	* lang.opt (std=legacy): New F95 command line option.
> 	* invoke.texi: Document both -std=f2003 and -std=legacy.
> 	* gfortran.texi: Explain the two types of extensions and document
> 	how they are affected by the various -std= command line options.

Ok.

Paul