save shared state in backup
if purchase is shared check before making the payment of before claim the order
already confirmed order can return without effective if coin selection was not made
sharePayment operation
This request supersedes the abortPayWithRefund request, as that's too
implementation-focused and does not describe well what's happening.
Also, abortPay can be forced to transition a transaction immediately
into an "aborted" state (either from "paying" or "aborting").
