0.9.15.17:

0.9.15.17:
	OK then.  Fix %INSTANCE-TYPEP deftransform
	... if we're testing for a structure-classoid, then any object
		with an invalid layout is neccessarily not typep that
		class.
	... if we're testing for something with a fixed depthoid (i.e.
		something which is always at a given position in the
		layout-inherits), then if we get an object with an
		invalid layout we mustn't throw an error before trying
		to update the object.