typeck.c (convert_for_assignment): Converting from pm of vbase to derived is an error...

typeck.c (convert_for_assignment): Converting from pm of vbase to derived is an error, not a sorry.

	* typeck.c (convert_for_assignment): Converting from pm of vbase
	to derived is an error, not a sorry.
	* call.c (build_over_call): Use convert_pointer_to_real for 'this'.
	* class.c (fixed_type_or_null): Rename from
	resolves_to_fixed_type_p.  Return the dynamic type of the
	expression, if fixed, or null.
	(resolves_to_fixed_type_p): Use it.  Return 0 if the dynamic type
	does not match the static type.
	(build_vbase_path): Rename 'alias_this' to 'nonnull'.  Use
	resolves_to_fixed_type_p again.

From-SVN: r21958