[PATCH] moving some of slab allocator declarations to header files

This patch moves most part of generic slab allocator declarations to new 
header files kmem_cache.h and kmem_slab.h, which can be usefull for 
debuging and making code more splitted from decls.
It doesn't change any functionality.

Signed-Off-By: Kirill Korotaev <dev@sw.ru>

Kirill