Investigate revision reconstruction discrepancy with subversion export

When trying to load again some subversion repositories into the archive, the loader detects that the history got altered and abort the loading process, see #3694 (closed) and related sentry issue.

For some rare cases, it can come from the subversion history being rewritten server side using svnadmin command but most of the times it means that the filesystem associated to a revision and reconstructed using the svn_ra API diverges from the one obtained by a svn export operation on the same revision.

Let's try to analyze and fix those issues in that task.

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Migrated from T3695 (view on Phabricator)