Hi,

I submitted a previous version of this patch yesterday, only to find
that making last minute changes is a big fat no no. Anyhow, having fixed
the two problems I found, I also added the tests I should have written
and run before sending my patch.

Best,
Rutger

Content of previous email below:

This patch replaces open-process with piped-process in posix.c and
reimplement open-process with piped-process in popen.scm. This allows
setting up a pipeline in guile scheme using the new pipeline procedure
in popen.scm and enables its use on operating systems which happen to
lack the capability to fork, but do offer the capability captured by
start_child (see posix.c).

The snippet below demonstrates the backwards compatibility of this patch
as well as the feature it offers:

(use-modules (ice-9 popen))
(use-modules (ice-9 rdelim))
(use-modules (ice-9 receive))

(receive (from to pid)
    ((@@ (ice-9 popen) open-process) OPEN_BOTH "rev")
  (display "dlrow olleh" to) (close to)
  (display (read-string from)) (newline)
  (display (status:exit-val (cdr (waitpid pid)))) (newline))

(receive (from to pids)
    (pipeline '(("echo" "dlrow olleh") ("rev")))
  (display (read-string from))
  (display (map waitpid pids)) (newline))

(let ((p (pipe)))
  (piped-process "echo" '("foo" "bar")
                 (cons (port->fdes (car p))
                       (port->fdes (cdr p))))
  (display (read-string (car p))))