This is a regression introduced by commit d5493fe894
[threadutil: explicitly import get_ident from thread].
The threadid attribute was wrongly removed from the ExitNotifyThread class.
Restore it.
Tested-by: Mark Foxwell <fastfret79@archlinux.org.uk>
Reviewed-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>