Fix infinite recursive signatures.

Such as this, submitted by Torsten Grust:

(define-record-procedures-parametric stream_ stream-of
  make-stream
  stream?
  (stream-head stream-tail))

(define stream
  (lambda (t)
    (signature (stream-of t (-> (stream t))))))

(: from (number -> (stream number)))
(define from
  (lambda (n)
    (make-stream n (lambda () (from (+ n 1))))))

(: foo (stream number))
(define foo (from 1))

The problem was that the arbitaries got evaluated too eagerly.

collects/deinprogramm/define-record-procedures.scm

@@ -189,14 +189,15 @@
 										 type-descriptor raw-predicate
 										 sigs
 										 #'?type-name)))
+						 (set-signature-arbitrary-promise! 
+						  sig
+						  (delay
 						    (let ((arbs (map signature-arbitrary sigs)))
 						      (when (andmap values arbs)
-						     (set-signature-arbitrary! 
-						      sig
 							(apply arbitrary-record
 							       ?constructor
 							       (list raw-accessor-proc ...)
-							     arbs))))
+							       arbs)))))
 						 sig)))
 				       'stepper-skip-completely
 				       #t)))

collects/deinprogramm/signature/signature.rkt

@@ -4,7 +4,7 @@
 	 signature-name signature-syntax signature-enforcer
 	 signature-arbitrary-promise
 	 signature-<=?-proc signature-=?-proc
-	 signature-arbitrary set-signature-arbitrary!
+	 signature-arbitrary set-signature-arbitrary! set-signature-arbitrary-promise!
 	 signature-info-promise
 	 signature-violation
 	 signature-violation-proc call-with-signature-violation-proc