snapshot: try to refine new snapshot base down the chain...
snapshot: try to refine new snapshot base down the chain
There are cases where doing a diff against a snapshot's parent will be shorter
than against the snapshot itself. Reusing snapshot not directly related to the
revision we are trying to store increase this odd.
So once we found a possible candidate, we check the snapshots lower in the
chain.
This will involve extra processing, but this extra processing will only happen
when we are doing building a snapshot, a rare situation.
