As the subject says.  I mostly use `git annex sync --content` to transfer
files between repositories, as its easier than running `git annex sync`, a
bunch of `git annex copy`s and then a `git annex get` to make sure I have
all the files I should have.  It would be good if the shortcut could also
work in parallel.

> It also can be faster to push concurrent. OTOH, concurrent pulls
> can lead to the same git objects being downloaded redundantly, so best to
> avoid those I think.
> 
> I've implemented this. It suffers from the same
> lack of support for displaying progress when running it parallel as
> documented on [[parallel_get]]. Other than that wart, this is [[done]].
> --[[Joey]]
