* Fix PRETask serialization
* Use a constant for encrypted kfrag length
* Fix argument order in Signature.verify()
* Remove a too brittle check in test_bob_handles_frags
What exactly are we ensuring here? If we want to check that the cfrag is fine,
we need to use it for decryption.
* Remove an unnecessary check
The result of `reencrypt()` is verified by default.
* Re-raise Umbral decryption errors as DecryptionFailed
* Fix an argument of _filter_work_orders_and_capsules()
* Fix an assertion in test_federated_grant_and_revoke
Assertion fails because now UmbralMessageKit has __len__,
so a bool() call is equivalent to len() == 0
(which it is, since there are no cfrags attached).