1.0.14.30: don't construct obsolete instances

1.0.14.30: don't construct obsolete instances
	The CTOR make-instance optimization machinery closes over the
	class wrapper of the class in question; however, there are
	code paths that cause wrappers to be invalidated without causing
	all constructors to be recomputed: for instance, the
	redefinition of a superclass, or calling
	MAKE-INSTANCES-OBSOLETE.  This would mean that the CTORs would
	create obsolete instances, which would instantly trap, showing
	up as slowness in CLOS-heavy code.

	Problem and fix largely identified by Andy Hefner in
	<http://paste.lisp.org/display/55689>.