* extend.texi (Deprecated Features): New node.
	* invoke.texi (-Wdeprecated): Document.
	* cp/lang-options.h (-Wdeprecated): New flag.
	* cp/decl2.c (warn_deprecated): New flag.
	(lang_decode_option): Deprecated this-is-variable,
	external-templates, alt-external-templates.
	Support -Wdeprecated.
	* cp/errfn.c (cp_deprecated): New function.

From-SVN: r26438