[Suspend2] Freezer Upgrade Patches

Hi everyone.

This set of patches represents the freezer upgrade patches from Suspend2.

The key features of this changeset are:

- Use of Christoph Lameter's todo list notifiers, which help with SMP
  cleanness.
- Splitting the freezing of kernel and userspace processes. Freezing
  currently suffers from a race because userspace processes can be
  submitting work for kernel threads, thereby stopping them from
  responding to freeze messages in a timely manner. The freezer can
  thus give up when it doesn't really need to. (This is not normally
  a problem only because load is not usually high).
- The use of bdev freezing to ensure filesystems are properly frozen,
  thereby increasing the integrity of on-disk data in the case where
  a resume doesn't occur. This is also helpful in the case of Suspend2,
  where we don't atomically copy all memory, instead writing LRU pages
  separately.

Signed-off-by: Nigel Cunningham <nigel@suspend2.net>

--
Nigel Cunningham   nigel at suspend2 dot net   http://suspend2.net