um: Run UML in it's own session.

If UML is not run by a shell it can happen that UML
will kill unrelated proceses upon a fatal exit because
it issues a kill(0, ...).
To prevent such oddities we create a new session in main().

Reported-and-tested-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/main.c

@@ -123,6 +123,8 @@ int __init main(int argc, char **argv, char **envp)
 
 	setup_env_path();
 
+	setsid();
+
 	new_argv = malloc((argc + 1) * sizeof(char *));
 	if (new_argv == NULL) {
 		perror("Mallocing argv");