IncrementalVerifier moved to Utility.Hash, which will let Utility.Url
use it later.
It's perhaps not really specific to hashing, but making a separate
module just for the data type seemed unncessary.
Sponsored-by: Dartmouth College's DANDI project
Added fileRetriever', which will let the remaining special remotes
eventually also support incremental verify.
Sponsored-by: Dartmouth College's DANDI project
The goal is that Database.Keys be able to use it; it can't use
Annex.Content.Presence due to an import loop.
Several other things also needed to be moved to Annex.Verify as a
conseqence.
Transfers from or to a local git repo could fail without a reason being
given, if the content failed to verify, or if the object file's stat
changed while it was being copied. Now display messages in these cases.
Sponsored-by: Jack Hill on Patreon
