Add missing export in SRFI-42, reported by Will Farr

svn: r1184

collects/srfi/42/comprehensions.ss

@@ -14,6 +14,7 @@
     : :list :string :vector :integers :range :real-range :char-range 
       :port :dispatched :do :let :parallel :while :until
     :-dispatch-ref :-dispatch-set! make-initial-:-dispatch 
+    dispatch-union
     :generator-proc )
 
 ; There is a subtle point in defining a macro inside a module 
@@ -1000,4 +1001,4 @@
      (first-ec #t qualifier (if (not expression)) #f) )))
 
 ; ec.scm with 'define-syntax-globally ends here ----------------------------
-) ; close the module
+) ; close the module