* Migrate callbacks registered under provisional (tx-output tuples) keys
as soon as their txids are known. Leave a txid breadcrumb in place so
register_callbacks and check_callback_called can find it and the
migrated list of callbacks.
* Invoke callbacks via list comprehensions, retaining only the callbacks
that return False. The old code was buggy, as it was removing elements
from the callback lists while iterating over them, which would cause
callbacks to be skipped.
* The existing code would fail to call any "confirmed" callbacks for a
remove-only transaction if no "unconfirmed" callbacks had been
registered for that transaction, and it would discontinue monitoring
of a transaction after just one "confirmed" callback had returned
True, even if other "confirmed" callbacks returned False to remain
registered. This commit overhauls the logic to fix all of these bugs.
* Delete emptied callback lists from the dicts to be tidy.
Matt Whitlock
8fe5b7b712