[Gzz] PEG 1017

[Tuomas Lukka]

> Of course we can leave public depth attribute as it is and 
> make new BFRaster.read() simple to give it a new value and call
> the old read().

Hmm. The only use for the depth is when you get handed a BFRaster
and want to know how deep it goes.

I'd prefer BFRaster.read taking it as a parameter and writing
it into the attribute for other to *read*. Writing to the attribute
would be deprecated (the others are read-only, too ... maybe you
should document that in the PEG as well?)

        Tuomas