u9fs: map client's user "none" to server's user "nobody" if "none" is not there.

Reference: /n/sources/patch/applied/u9fs-nobody
Date: Thu Jul  7 16:15:32 CES 2011
Signed-off-by: yarikos@gmail.com

--- /sys/src/cmd/unix/u9fs/u9fs.c	Thu Jul  7 16:12:52 2011
+++ /sys/src/cmd/unix/u9fs/u9fs.c	Thu Jul  7 16:17:54 2011
@@ -401,6 +401,7 @@
 			seterror(tx, Eauth);
 			return;
 		}
+		rx->uname = none->name;
 	} else {
 		if((e = auth->attach(rx, tx)) != nil){
 			seterror(tx, e);
@@ -1759,6 +1760,8 @@
 			sysfatal("chroot '%s' failed", argv[0]);
 
 	none = uname2user("none");
+	if(none == nil)
+		none = uname2user("nobody");
 
 	serve(0, 1);
 	return 0;