with Debian dir 13f2cc753f39dbbff732279ae6a48ecf4a9516e4

Needed by the replayer in swh-journal.

with Debian dir da13c61a77431bbfd0ffb08fff8fcdfed1989d4e

with Debian dir 2e23d1f94249265cf074e48e4d9f41f9aa7574e8

It kind of matches the current state of the postgresql storage, which
does not support it.

But keep support for deserializing from str, like
swh-storage does.

with Debian dir 61ff8c95c9f4d4dcb1f4f60fdc85584fb19af9ad

Code manipulating a Content object may want to access a hash
of configurable name; this method allows it to do that
without using getattr directly.

It denotes files whose length is unknown.

with Debian dir 91bc9fdc9b1362cd03827038fbbd596cc1b78e62

with Debian dir a21bc9196b874697507e45ed0c1f9394ddcf7bb3

Loaders use it, but it is ignored by the pg storage.
However, as the Cassandra storage uses swh-model to validate
its input, it refuses this input from the loaders (and journal).

Remove version checking code, pyblake2 is installed by default on python 3.6+