Option to deactivate file system attachment versioning not taken into account

Steps to reproduce:

• Use the default attachment storage, i.e. "file"
• Deactivate file attachment versioning in xwiki.cfg:

  xwiki.store.attachment.versioning=0

• Upload new file to a page, and again
• Display the attachment history by hitting the "1.2" revision number next to the attachment
• Two versions of the attachment are listed, while only one would be expected