Cryptonite is faster and allocates less, and I want to get rid of
MissingH use.
Note that the new dependency on memory is free; it's a dependency of
cryptonite.
This commit was supported by the NSF-funded DataLad project.
Note that get --from foo --failed will get things that a previous get --from bar
tried and failed to get, etc. I considered making --failed only retry
transfers from the same remote, but it was easier, and seems more useful,
to not have the same remote requirement.
Noisy due to some refactoring into Types/
