This moves refrigerator changes to sched.h, so that every file user of
refrigerator does not have to include suspend.h, and makes refrigerator
support easier by introducing try_to_freeze.

Adapted from patch by Nigel Cunningham
Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>