We cannot reuse the replay functionality to come to the same state.
So we use the following steps:
- checkout on disk at given revision
- walk the disk and compute hashes

Check the hashes' revision match.
If they do, we already injected.
Otherwise:
- either the svn history got modified and we stop at that.
- either we change the swh-loader-svn's options (commit extra
line on/off, empty folder policy on/off, etc...)

Create ra.SWHReplay class to reuse code and clarify intent

(This code was actually lost and rewritten from memory)

Delegate to swh.model.git module