Introduce a new tree, dedupe tree to record on-disk dedupe hash.
As a persist hash storage instead of in-memeory only implement.
Unlike Liu Bo's implement, in this version we won't do hack for
bytenr -> hash search, but add a new type, DEDUP_BYTENR_ITEM for such
search case, just like in-memory
Introduce a new tree, dedupe tree to record on-disk dedupe hash.
As a persist hash storage instead of in-memeory only implement.
Unlike Liu Bo's implement, in this version we won't do hack for
bytenr -> hash search, but add a new type, DEDUP_BYTENR_ITEM for such
search case, just like in-memory
