if creating a new process, RFNOMNT applies to child.

Reference: /n/patches.lsub.org/patch/rfnomntp
Date: Sun Oct 28 17:23:57 CET 2012
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/sysproc.c	Sun Apr 15 19:46:44 2012
+++ /sys/src/nix/port/sysproc.c	Sun Oct 28 16:28:12 2012
@@ -165,7 +165,7 @@
 		incref(p->pgrp);
 	}
 	if(flag & RFNOMNT)
-		up->pgrp->noattach = 1;
+		p->pgrp->noattach = 1;
 
 	if(flag & RFREND)
 		p->rgrp = newrgrp();