replay: Prevent erroneous removal of versioned path
When processing an external, the content of the target directory is first removed before copying external dirs and files.
But that target directory might contain versioned paths so we must ensure to restore them after removing the directory content.
Related to #611
Fixes some events in SWH-LOADER-SVN-53
Depends on !117 (closed)
Migrated from D7091 (view on Phabricator)