We have three arrays for thread related data: item->threads,
parasite_ctl->thread and tid_state in parasite.

With this patch a thread will have the same index in all arrays.
The zero index is used for a thread leader.

In this case we don't need to search thread_state in parasite.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>