mveety — don't fault if not given expected arguments

Reference: /n/atom/patch/applied2013/authasargs
Date: Tue Jun 18 00:35:44 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/auth/as.c	Tue Jun 18 00:34:54 2013
+++ /sys/src/cmd/auth/as.c	Tue Jun 18 00:34:54 2013
@@ -52,7 +52,10 @@
 
 	initcap();
 	srand(getpid()*time(0));
-	runas(argv[0], argv[1]);
+	if(argc >= 2)
+		runas(argv[0], argv[1]);
+	else
+		usage();
 }
 
 void
@@ -88,7 +91,7 @@
 void
 usage(void)
 {
-	fprint(2, "usage: %s [-c]\n", argv0);
+	fprint(2, "usage: %s [-c] user cmd\n", argv0);
 	exits("usage");
 }