When a transaction is received by the p2pnet layer via a simple INV/
GetData we now process this and properly lock the outputs it spent to
avoid creating double spending transactions.
One task is left: properly recognize when a mined transaction
invalidates another transaction (like an unconfirmed one) and update the
datastructures.
The code to re-org all transactions in a block so transactions that
depend on others are processed after those they depend on had a silly
bug (missing line), fixed that but also made it unit-testable to
demonstrate the bug.