18.104.22.168: 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
... test case.