From: Nigel Cunningham <ncunningham@users.sourceforge.net>

A few weeks ago, Pavel and I agreed that PF_IOTHREAD should be renamed to
PF_NOFREEZE.  This reflects the fact that some threads so marked aren't
actually used for IO while suspending, but simply shouldn't be frozen.
This patch, against 2.6.5 vanilla, applies that change.  In the
refrigerator calls, the actual value doesn't matter (so long as it's
non-zero) and it makes more sense to use PF_FREEZE so I've used that.