How to make iPhoto library back into bundle
EDIT: Changed my answer.  :-)

I copied my iPhoto Library, and removed the extended attributes (a piece of metadata called com.apple.finderInfo). It then showed up as a folder rather than a proper iPhoto Library. I then fired up iPhoto holding option, and selected this folder as my iPhoto Library. It accepted it and changed the type, putting the metadata back, and all was well. I suspect this is what needs to happen in your case as well, it looks like as long as the files are there, iPhoto will do the work for you. 

Old answer: I think you can rename it to 'iPhoto Library.bundle'.  It will then take the form of a bundle.  You can then remove the '.bundle' from the file name and it should (still) act bundle-like.

Not really sure though.

EDIT: or .app