Remove reliance on accounting "move" ledger entries. Instead,
create funding transactions (and deal with fee complexities).
Do not rely on broken SyncMetaData. Instead expect double-spend
amount to be debited from the default "" account.
Ported txnmall.sh to Python, and updated to match
recent transaction malleability changes.
I also modified it so it tests both double-spending
confirmed and unconfirmed (only-in-mempool) transactions.
Renamed to txn_doublespend, since that is really what is
being tested. And told the pull-tester to run both
variations on this test.
