There was an atomicity problem/race condition -- if a child process died

after it was forked, but before the scsh fork procedure could register
the child's procobj in the pid/procobj table, then when the SIGCHLD
signal-handler reaped the process, there would be no procobj for it.
We now lock out interrupts across the fork and register operations.

scsh/procobj.scm

@@ -314,7 +314,7 @@
 				       reaped-procs))
 	      (lambda () #f)))
 	   (else (lambda ()	; Do this w/interrupts enabled.
-		   (error "Child pid mysteriously missing proc object." pid)))))))
+		   (warn "Exiting child pid has no proc object." pid status)))))))
   
 ;;; Pop one off the list.
 (define (get-reaped-proc!)

scsh/scsh.scm

@@ -702,14 +702,21 @@
   (really-fork #f maybe-thunk))
 
 (define (really-fork clear-interactive? maybe-thunk)
-  (let ((pid (%%fork)))
-    (cond ((zero? pid)				; Child
-	   (set! reaped-procs '())
-	   (if clear-interactive?
-	       (set-batch-mode?! #t))	; Children are non-interactive.
-	   (and (pair? maybe-thunk)
-		(call-terminally (car maybe-thunk))))
-	  (else (new-child-proc pid)))))	; Parent
+  ((with-enabled-interrupts 0
+     (let ((pid (%%fork)))
+       (if (zero? pid)				
+
+	   ;; Child
+	   (lambda ()	; Do all this outside the WITH-INTERRUPTS.
+	     (set! reaped-procs '())
+	     (if clear-interactive?
+		 (set-batch-mode?! #t))	; Children are non-interactive.
+	     (and (pair? maybe-thunk)
+		  (call-terminally (car maybe-thunk))))
+
+	   ;; Parent
+	   (let ((proc (new-child-proc pid)))
+	     (lambda () proc)))))))
 
 
 (define (exit . maybe-status)