[plt-scheme] 203.3

The exp-tagged code in CVS for MrEd and MzScheme is now version 203.3.

The change is a minor addition:

 * Added `make-rename-transformer', which takes a syntax identifier
   <id> and produces a macro transformer that replaces an identifer
   bound to the transformer with <id>.

   The `make-rename-transformer' procedure cooperates specially with
   `syntax-local-value'. When finding the expansion-time value for an
   identifier, `syntax-local-value' chains through rename transformers.

   Example use:

     (define-struct s (a b))
     (define-syntax t (make-rename-transformer #'s))
     (define-struct (sub-s t) (c))
     ;; `sub-s' is derived from `s'

Matthew