Hi.

The attched patch adds the PR_DETACH prctl command.
It is needed for those rare but unfortunate cases, where
you can't daemonize your process before creating a thread.
The effect of this command is similar to the fork() and then
exit() on parent, except that:
1. PID does not change
2. Threads are not destroyed

It would be nice to know what people think about such an
approach.

Signed-off-by: stsp@aknet.ru
CC: Oleg Nesterov <oleg@redhat.com>