DR 1207
	PR c++/49589
	* mangle.c (write_expression): Handle 'this'.
	* parser.c (cp_parser_postfix_dot_deref_expression): Allow
	incomplete *this.
	* semantics.c (potential_constant_expression_1): Check that
	DECL_CONTEXT is set on 'this'.

From-SVN: r175835