Our existing coin_moves tracking logic assumed that any tx we had an
input in belonged to *all* of our wallet (not a bad assumption as long
as there was no way to update a tx that spends our wallets)
Now that we've got `signpsbt` implemented, however, we need to be
careful about how we account for withdrawals. For now we do a best guess
at what the feerate is, and lump all of our spent outputs as a
'withdrawal' when it's impossible to disambiguate
niftynei
2e9c387f45