We try to display attachments in feed even for users who don't have the right to see them

In any feed, if an user doesn't have the permission to see the attachments of the displayed topic, we parse the [attachment]'s tags to display the attachment, instead of displaying the text that is between the tags.
So if the attachment isn't displayed it's only because '/download/file.php' verify the permissions.

I think that we should display the text that is between the tags (as in viewtopic.php).