Equal should not check attestations

[LeoComandini]

To be consistent with python-opentimestamps, when checking if two timestamps are equal, attestations should not be checked.

[petertodd]

Actually, that sounds like a mistake in python-opentimestamps; I can't think of a good reason for equality to ignore attestations. -- https://petertodd.org 'peter'[:-1]@petertodd.org