These are unlikely to happen at random, but Wijaya et al made
a paper about it, so people might try it on purpose now (and it
turns out it's easy to add anyway)
This will avoid careless forkers polluting the shared database
even if they make their own chain. They'll then automatically
start using another subdb, and any key-reusing fork of those
forks will reuse their subdbs.
It scans for known spent outputs and stores their public keys
in a database which can then be read by the wallet, which can
then avoid using those as fake outs in new transactions.
Usage: monero-blockchain-blackball db1 db2...
This uses the shared database in ~/.shared-ringdb
