Just exec() the command, rather than calling it with system() - this

way, we don't have to worry about sshtb getting killed but its child
process hanging around.

utils/sshtb.in

@@ -111,10 +111,4 @@ else {
 if ($debug) {
     print "$cmd\n";
 }
-system("$cmd");
-
-if ($debug) {
-    print "Exited with $CHILD_ERROR\n";
-}
-
-exit($CHILD_ERROR >> 8);
+exec("$cmd");