I noticed that swsusp uses quite a few interesting casts for __pa() and
cousins.  This patch moves some types around to eliminate some of those
casts in the normal code.  The casts that it adds are around alloc's and
frees, which is a much more usual place to see them.  

Pavel also noticed that there's a superfluous PAGE_ALIGN() right before
a >>PAGE_SHIFT in pfn_is_nosave(), so that's been removed as well.

I haven't had a chance to do anything but test it, because that would
involve me setting up a swsusp rig, which I'm more prone to screw up
than the patch itself :)  I'd appreciate if anyone with a stable setup
could make sure I didn't do anything too stupid.  

-- Dave