git chokes when pushing very large commits

[achilleas-k]

When a commit is very large (over 4 GiB it seems) it's possible that it becomes impossible to push. This can occur (and has occurred) in repositories where a lot (thousands) of files are below the annex threshold (10 MiB by default) but together are multiple GiB in size, creating a single very large commit.

It would be good if we could have a way to warn the user about this and ask them to make multiple smaller commits. It might be even better if gin-cli could do it for them (?).