exposed pipeline patch (long!)

[Doug Evans]

Ben Elliston writes:
 > I'm posting this patch on behalf of Graydon Hoare, who write this
 > exposed pipeline support last year.  It's a more generalised form of
 > the (delay ..) rtx and has been used for a couple of ports already.

Also, nit.  I'd rather not add seq when there's already iota.

 > Index: utils.scm
 > +(define (seq p q) (if (> p q) '() (cons p (seq (+ p 1) q))))