[PATCH] mm: update stale comment for removal of page->list

Update comment for the 2.6.6-rc1 conversion from page->list and
address_space->{clean,dirty,locked}_pages to radix tree tagging and ->lru.

I've mostly avoided to mention page lists (at least I've shortened the
comment).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>