gfortran.h (GFC_STD_LEGACY): New "standard" macro.

	* 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.

From-SVN: r100377