Only increment new notes on reindex
Addresses another issue in #1904.
When an existing one of our notes was found again, its cache was reset and it was re-witnessed. This would cause encountered notes to get out-of-sync with the otherwise-ignored newer notes, which could be a problem if the wallet data happens to be written out during a reindex.
Write witness caches when writing the best block
For steady-state operation, this reduces the average time between wallet disk
writes from once per block to once per hour.
On -rescan, witness caches are only written out at the end along with the best
block, increasing speed while ensuring that on-disk state is kept consistent.
Witness caches are now never recreated during a -reindex, on the assumption that
the blocks themselves are not changing (the chain is just being reconstructed),
and so the witnesses will remain valid.
Part of #1749.
Isolate verification to a ProofVerifier context object that allows verification behavior to be tuned by the caller.
This is an alternative foundation for #1892, i.e., #1892 will have to be changed if this PR is accepted.
I think this is a safer approach because it allows us to isolate verification behavior to a single object. This will come in handy when @arielgabizon finishes the batching code.
For steady-state operation, this reduces the average time between wallet disk
writes from once per block to once per hour.
On -rescan, witness caches are only written out at the end along with the best
block, increasing speed while ensuring that on-disk state is kept consistent.
Witness caches are now never recreated during a -reindex, on the assumption that
the blocks themselves are not changing (the chain is just being reconstructed),
and so the witnesses will remain valid.
Part of #1749.
