sched: kernel threads shouldn't keep reference to any app

It is possible that an application thread causes a creation of a kernel
thread (e.g. some ZFS related ioctls tend to do that). Such threads
shouldn't keep reference to the application of the thread that spawned
them since that may needlesly defer the destructon of such application.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
runtime: Remove duplicate libintl.h include

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>