Comment 0 for bug 309066

  When redefining an accessor, SB-PCL::FIX-SLOT-ACCESSORS may try to
  find the generic function named by the old accessor name using
  ENSURE-GENERIC-FUNCTION and then remove the old accessor's method in
  the GF. If the old name does not name a function, or if the old name
  does not name a generic function, no attempt to find the GF or remove
  any methods is made.

  However, if an unrelated GF with an incompatible lambda list exists,
  the class redefinition will fail when SB-PCL::REMOVE-READER-METHOD
  tries to find and remove a method with an incompatible lambda list
  from the unrelated generic function.