Transactions in the txpool are marked when another transaction
is seen double spending one or more of its inputs.
This is then exposed wherever appropriate.
Note that being marked with this "double spend seen" flag does
NOT mean this transaction IS a double spend and will never be
mined: it just means that the network has seen at least another
transaction spending at least one of the same inputs, so care
should be taken to wait for a few confirmations before acting
upon that transaction (ie, mostly of use for merchants wanting
to accept unconfirmed transactions).
m_amount_out was sometimes getting initialized with the sum of
an transaction's outputs, and sometimes with the sum of outputs
that were not change. This caused confusion and bugs. We now
always set it to the sum of outputs. This reverts an earlier
fix for bad amounts as this used the other semantics. The wallet
data should be converted automatically in a percentage of cases
that I'm hesitant to estimate. In any case, restoring from seed
or keys or rebuilding the cache will get it right.
