tty: Use separate tty_info::inherit member to track ttys being borrowed from a parent
tty: Use separate tty_info::inherit member to track ttys being borrowed from a parent

This is easier for debugging, the former SID/PGID remains untouched
and printed out in logs.

Signed-off-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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