[elephant-devel] derived indices

[Alex Mizrahi]

New derived index API is pretty nice, but it looks like implementation isn't 
quite mature.

Particularly, I've encountered a problem with redefinition -- when derived 
index definition in class changes
nothing changes.

Besides that, there is no analog of rebuild-slot-indices/rebuild-slot-index 
for derived index.

So to use them you have to do it right from start.