MFC revision 1.290

Hopefully close up race between the TTY (t_session) subsystem and exit(2)

date: 2006/09/13 15:47:53; author: csjp; state: Exp; lines: +2 -2
Back out one of the Giant removals from revision 1.272. Giant was not here to
protect the vnode, it was present to synchronize access to TTY session
information between exit(2) and the TTY code. While we are here, note that
Giant is required for TTY protection.

Clue from: bde
Discussed with: jhb
Approved by: re@ (mux)