1.0.5.47: cacheability of EMFs from methods with non-standard specializers

1.0.5.47: cacheability of EMFs from methods with non-standard specializers
	... the second return value from
	COMPUTE-APPLICABLE-METHODS-USING-CLASSES promises that the
	first return value can be cached.  It doesn't promise that an
	arbitrary computation on the specializers will work, so we need
	not to go down that codepath.
	... so refuse to build dispatch discriminating functions if any
	method of the generic function has a non-standard
        (non-PCL-native) specializer, as operations such as
	SB-PCL::SPECIALIZER-CLASS and SB-PCL::TYPE-FROM-SPECIALIZER
	will fail on such specializers
	... rework SPECIALIZER-CLASS-OR-NIL to call the new function
	STANDARD-SPECIALIZER-P.
	... test case.