Renames Update to SignedBatch.
Checks Batch equality via a hash of the InInstructions. That prevents needing
to keep the Batch in node state or TX introspect.
Due to the ordered message-queue, there's no benefit to multiple emissions as
there's no risk a completion will be missed. If it has yet to be read, sending
another which only be read after isn't helpful.
Simplifies code a decent bit.
