Enable custom wallet filename
Add improvements suggested by domob1812
fix double path in wallet backup
Merge pull request #121 from digital-dreamer/custom-wallet-filename

Custom wallet filename option
changelog.md: walletpath
Start with UTXO database implementation.

Start with the implementation of a UTXO set database for tx
verification.  This is a squashed commit of the old utxo branch after
rebasing it onto the DatabaseSet changes.
Update the UTXO set in DisconnectInputs.

Also handle the UTXO set in DisconnectInputs.  Not yet really tested.
Skip unspendable outputs in UTXO set creation.

For certain types of unspendable outputs (network fee OP_RETURN scripts
as well as names that have been expired at the last checkpoint), don't
include the tx outputs in the UTXO set.
Make IsUnspendable accept the CTxOut directly instead of the script.