SLAB allocator now the default.

[Matthew Dillon]

    The slab allocator is now the default.  The NO_KMEM_MAP and
    USE_SLAB_ALLOCATOR options have been removed.

    USE_KMEM_MAP and NO_SLAB_ALLOCATOR options have temporarily been added,
    but these too will be removed (along with the old malloc and kmem_map
    code) in about a week.

						-Matt