Fix argument passing for external hash functions in `(rnrs hashtables)'.

Guile implements this library in terms of SRFI-69, which is a bit vague on
the arity of hash functions, whereas `(rnrs hashtables)' explicitly
specifies unary ones.

* module/rnrs/hashtables.scm (wrap-hash-function): Assume SRFI-69 will pass
  the table capacity as the second argument; return the result of proc
  modulo the capacity.

* test-suite/tests/r6rs-hashtables.test (make-hashtable): New test case for
  hash functions that return large values.

module/rnrs/hashtables.scm

@@ -45,7 +45,8 @@
   (import (rename (only (guile) string-hash-ci 
                                 string-hash 
                                 hashq 
-                                hashv 
+                                hashv
+                                modulo
                                 *unspecified*
                                 @@)
 		  (string-hash-ci string-ci-hash))
@@ -88,7 +89,8 @@
   (define hashtable-mutable? r6rs:hashtable-mutable?)
 
   (define hash-by-value ((@@ (srfi srfi-69) caller-with-default-size) hashv))
-  (define (wrap-hash-function proc) (lambda (key obj) (proc key)))
+  (define (wrap-hash-function proc) 
+    (lambda (key capacity) (modulo (proc key) capacity)))
 
   (define* (make-eq-hashtable #:optional k)
     (make-r6rs-hashtable 

test-suite/tests/r6rs-hashtables.test

@@ -45,7 +45,13 @@
 	   (abs-hashtable (make-hashtable abs abs-eqv?)))
       (hashtable-set! abs-hashtable -4 #t)
       (and (not (hashtable-contains? abs-hashtable 6))
-	   (hashtable-contains? abs-hashtable 4)))))      
+	   (hashtable-contains? abs-hashtable 4))))
+
+  (pass-if "hash function value used modulo capacity"
+    (let* ((constant-hash (lambda (x) most-positive-fixnum))
+	   (constant-hashtable (make-hashtable constant-hash eq?)))
+      (hashtable-set! constant-hashtable 'foo 'bar)
+      (hashtable-contains? constant-hashtable 'foo))))
 
 (with-test-prefix "hashtable?"
   (pass-if "hashtable? is #t on hashtables"