Sequences in reverse order

In the Corgi testnet, there are invalid transactions found on the block [29978](http://corgi.codechain.io/explorer/block/29978) and 29979

In block 29978, there are 2 transactions which were signed by the same signer.

The sequence of the first tx(0x615f65...) is 42929 and it failed.
The sequence of the second tx is 42928.

In addition, the first tx(0x615f65..) appears again in the next block, which is 29979. (But, you wouldn't find it in the explorer because the indexer can't index it.)

Start by reproducing the transaction ordering in Corgi testnet blocks 29978 and 29979, using the linked explorer and transaction prefix 0x615f65. Trace how sequence validation handles the two transactions and how the repeated transaction reaches the indexer; done means the invalid ordering and duplicate appearance no longer occur and the affected transaction can be indexed.

Escrita pelo modelo de indexação a partir do texto da issue.