[PATCH] swsusp: update userland interface documentation

The swsusp userland interface has recently changed for a couple of times, but
the changes have not been documented.  Fix this, and document the
SNAPSHOT_SET_SWAP_AREA ioctl().

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>