[CRIU] [RFC 0/6] Migrate slave tty connections

[Cyrill Gorcunov]

Hi guys, please review. The patches 1,2 are safe to merge since
they only speedup current code. The rest are doable. Also, note,
that once ttys are restored we will fail on subsequent dumps since
we don't know yet how to dump /dev/tty device.

The main question if this approach is correct in general. The
problem is that when a user dumps only a part of process tree
we have a bit incomplete information available (no master
peers and as result no pgrp/sid can be fetched from such slave
peers).