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+

with Debian dir d6285282d0519bd3c16e020b63d01f4265c3da97

This is a fix to workaround pip's inability to correctly solve
extra requirements (swh-model depends on swh-core[], but if other
packages depend on swh-model and swh-core[http], the 'http' extra
does not always get installed).

with Debian dir ddca98e6157d1ca6e603aae3d7e3f42f298e9ce3

pgsql does not support it.

There is more repetition, but it's easier to read and
'%timeit Revision.from_dict(d)' is 5 times faster.