re PR c++/18064 (gcc accepts different pointer types as covariant return types)

re PR c++/18064 (gcc accepts different pointer types as covariant return types)

cp:
	PR c++/18064
	* search.c (check_final_overrider): Deprecate gnu covariant extension.
doc:
	PR c++/18064
	* doc/extend.texi (Deprecated Features): Deprecate G++ covariant
	extension.
testsuite:
	PR c++/18064
	* g++.old-deja/g++.mike/p811.C: Avoid covariant extension.

From-SVN: r89946