call-with-input-pipe, call-with-output-pipe: allow list argument

	The current implementation of both call-with-input-pipe and
	call-with-output-pipe uses /bin/sh to start the program
	specified, just like the system () call:

scheme48-99fb63e0ed13c-1/ $ nl -ba scheme/misc/pipe.scm
...
    29		       (lambda ()
    30			 (if input?
    31			     (remap-file-descriptors! (current-input-port)
    32						      output-pipe
    33						      (current-error-port))
    34			     (remap-file-descriptors! input-pipe
    35						      (current-output-port)
    36						      (current-error-port)))
    37			 (exec-file "/bin/sh" "-c" command))
    38		       (lambda ()
    39			 (exit 1)))))))))
scheme48-99fb63e0ed13c-1/ $ 

	Since it may be cumbersome to do all the shell quoting
	necessary, may I suggest to extend call-with-input-pipe and
	call-with-output-pipe to accept a list argument to be passed
	directly to exec?  Like:

foo> ,config ,load =scheme48/misc/packages.scm 
foo> ,open call-with-mumble-pipes 
foo> (call-with-input-pipe '("sha1sum" "--" "/dev/null") read-all)
"da39a3ee5e6b4b0d3255bfef95601890afd80709  /dev/null\n"
foo> 

	The change is as follows:

Extend `call-with-mumble-pipe' to allow list as an argument.
(call-with-mumble-pipe): Extended to accept a list argument to be passed
directly to `exec', instead of going through `/bin/sh'.

diff -r 99fb63e0ed13 scheme/misc/pipe.scm
--- a/scheme/misc/pipe.scm	Sun Oct 19 21:08:43 2008 +0200
+++ b/scheme/misc/pipe.scm	Tue Oct 21 00:14:14 2008 +0700
@@ -34,7 +34,11 @@
 		     (remap-file-descriptors! input-pipe
 					      (current-output-port)
 					      (current-error-port)))
-		 (exec-file "/bin/sh" "-c" command))
+		 (cond ((list? command)
+			(apply exec command))
+		       (else
+			;; FIXME: consider using "$SHELL" here
+			(exec-file "/bin/sh" "-c" command))))
 	       (lambda ()
 		 (exit 1)))))))))