cmap->index fails in generate-metadata.

[samrushing]

Ran into this problem:

(datatype lazy*
  (:delayed (-> 'a))
  (:value 'a)
  )

;; i.e. (ref (lazy 'a))
(typealias lazy {val=(lazy* 'a)})
...

(datatype stream
  (:nil)
  ;;(:cell 'a (lazy (stream 'a)))
  (:cell 'a {val=(lazy* (stream 'a))})
  )

The 'a from the typealias is not the same 'a in the datatype. The commented-out :cell arm thus causes a crash in dt.to-sexp in generate-metadata. Not sure if this is a simple problem with instantiation or if we need the ability to declare 'mutual' datatypes (with the idea that their type variables are the same).