free_pages_and_swap_cache() and free_page_and_swap_cache() use release_pages()
and page_cache_release() respectively, so make sure that we have the
declarations in scope.

Cc: Olaf Hering <olh@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>