dbpluginapi is an api to have plugins mark the database tables they introduce. That worked fine till I tried to support upgrade support, that just doesn't work with our approach to SQL (more than one database, no full layer abstracting the differences away, and writing real SQL). I asked Garvin how to salvage what is there, because the current solution for the database cleanup maintenance section is not nice. See https://github.com/s9y/Serendipity/issues/317, we'll talk about that later, possibly on the meeting.