replay: Handle recursive external definition
It is possible that an external definition lead to a recursive subversion export operation (https://issues.apache.org/jira/browse/SVN-1703).
As that recursive export will crash the loader and make the loading failed, the only solution for that edge case is to stop processing externals while a recursive external is detected in a revision.
We will then ignore externals when exporting a revision to check for divergence with the recontructed filesystem.
Related to #3870 (closed)
Migrated from D7027 (view on Phabricator)