- send 404 when feed id missing/unknown
- added a guid element for each feed item (make the difference between 2
different 0/1 items - they have the same link element)
- don't update last_check unless some news are available
- new images/updated albums removed from the 0/1 feed item
- added 5 different feed items for new images/updated albums (generated by
grouping post date) with more information, thumbnails and links
git-svn-id: http://piwigo.org/svn/trunk@1549 68402e56-0260-453c-a942-63ccdbb3a9ee