paintops

[Cyrille Berger]

> Any better ideas?
While looking at a way to optimize a little bit bristles, I had a closer look 
at this again tonight, and now it's clear to me that it is definitively the 
way to go, mostly because some paintop don't even have a notion of "spacing".

So unless someone object, I will make this change to the paintop soon, but 
only the paintAt will be pure virtual.

-- 
Cyrille Berger