clear out waiters list after fork

Reference: /n/atom/patch/applied2013/apeforkwait
Date: Fri Sep 20 16:29:55 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/ape/lib/ap/plan9/lib.h	Fri Sep 20 16:29:55 2013
+++ /sys/src/ape/lib/ap/plan9/lib.h	Fri Sep 20 16:29:55 2013
@@ -59,6 +59,7 @@
 extern void	_closebuf(int);
 extern int _readbuf(int, void*, int, int);
 extern void	_detachbuf(void);
+extern void	_nowaiters(void);
 extern void	_finish(int, char *);
 extern char	*_ultoa(char *, unsigned long);
 extern int	_notehandler(void *, char *);
--- /sys/src/ape/lib/ap/plan9/wait.c	Fri Sep 20 16:29:55 2013
+++ /sys/src/ape/lib/ap/plan9/wait.c	Fri Sep 20 16:29:55 2013
@@ -83,6 +83,12 @@
 	return (r<<8) | t;
 }
 
+void
+_nowaiters(void)
+{
+	wd = nil;
+}
+
 static void
 waitresource(struct rusage *ru, Waitmsg *w)
 {
@@ -123,7 +129,7 @@
 		if(options & WNOHANG){
 			snprintf(pname, sizeof(pname), "/proc/%d/wait", getpid());
 			d = _dirstat(pname);
-			if(d != nil && d->length == 0){
+			if(d == nil || d->length == 0){
 				free(d);
 				return 0;
 			}
--- /sys/src/ape/lib/ap/plan9/fork.c	Fri Sep 20 16:29:55 2013
+++ /sys/src/ape/lib/ap/plan9/fork.c	Fri Sep 20 16:29:55 2013
@@ -14,6 +14,7 @@
 	if(n == 0) {
 		_detachbuf();
 		_sessleader = 0;
+		_nowaiters();
 	}
 	return n;
 }