excluding noweb references completely from exports

[David Bremner <david@tethera.net>]

At the end you can find a cut down version of an org-mode file I am
using to generate some beamer slides. This works as written, but it
feels clumsy to use two src blocks for every snippet. I have tried
putting the <<include/animal-type.rkt>> in the main src block, but this
either generates a blank line or if I delete the newline after >>, the
export looks fine but the source is ugly to edit.

Any better ideas for how to do this? In case it's not clear, I want
include files in my tangled output that don't show in the beamer export.

Please CC me with any replies, I'm not on the list.

#+STARTUP: beamer
#+OPTIONS: toc:nil
#+PROPERTY: header-args :noweb strip-export :shebang "#lang plait" :tangle-mode (identity #o644)

#+BEGIN_SRC plait :tangle tangled.rkt :export none
<<include/animal-type.rkt>>
#+END_SRC
#+BEGIN_SRC plait :tangle tangled.rkt
#;(Snake 10 'Slimey 5)
; => compile error: 10 is not a Symbol

(Snake? (Snake 'Slimey 10 'rats)) ; => #t
(Snake? (Tiger 'Tony 12)) ; => #t
;(Snake? 10) 
             ; => compile error
#+END_SRC

#+NAME: include/animal-type.rkt
#+BEGIN_SRC plait :export none
(define-type Animal
  [Snake   (name : Symbol) (weight : Number) (food : Symbol)]
  [Tiger   (name : Symbol) (weight : Number)])

#+END_SRC