feature 1312 added: pwg.images.setInfo can replace multiple values propreties
(tags/categories). The primary condition is to provide "tag_ids" and/or
"categories" input parameters, ie pwg.images.set won't create emptiness. You
can reduce the set of tags/categories but not remove all tags/categories.
bug 1277 fixed: with a stronger algorithm for adding/replacing categories, we
now avoid to recreate an existing image_category association.
When a remote client calls pwg.images.setInfo, Piwigo returns an error 500 if:
1. the "categories" parameter is malformed (no numeric id inside)
2. one of the input categories does not exist at database level.
git-svn-id: http://piwigo.org/svn/trunk@4445 68402e56-0260-453c-a942-63ccdbb3a9ee