Performs general maintenance on attachments:
Removes attachments from the database if the file doesn't exist anymore
Recalculates filesize
Regenerates thumbnails if the thumbnail file for an attachment is missing

• Does not generate thumbnails for attachments that didn't originally have one (ie image attachments that were uploaded in earlier versions of SMF).
• Was called RecountAttachments() in 1.1 Beta 3 Public and 1.1 RC1