anchor.diff:    "Return all `Components` of `entity`.
      If `component-type` is specified, only the `Components` of `component-type`
      are returned otherwise all `Components` are returned."
  -  (with-existing-entity2 entity
  +  (with-existing-entity* entity
       (remove-if-not (lambda (x) (eql x entity)) 
                        (get-components-of-type component-type) 
                        :key #'entity)))
  
positive.code: 
  
  (defmethod (setf component-entity) (entity (component Component))
    (with-existing-entity2 entity
      (setf (slot-value component 'entity) entity)))
  
  
  
negative.code:   "Create a fresh-instance of `component-class` and add it to the components of 
     `entity`.
     `component-initargs` are supplied to `(make-instance component-class …)`."
    (with-existing-entity* entity
      (apply #'make-instance (append (list component-class :entity entity) component-initargs))))
  
  
  