XWIKI-7947: Attaching a file after a rollback restores previous attachments.

* Fix auto-cleaned import.
XWIKI-7947: Attaching a file after a rollback restores previous attachments.

* Fix the case when you upload a filed named like a previous deleted one and then you rollback to the previous.
XWIKI-7947: Attaching a file after a rollback restores previous attachments.

* Fix the case when you upload a filed named like a previous deleted one and then you rollback to the previous.
Merge pull request #187 from gdelhumeau/XWIKI-7947

 XWIKI-7947: Attaching a file after a rollback restores previous attachments.