[pypy-dev] 2.5 and 2.4 compatibility

I'm working on 2.5 compatibility branch right now. Due to incompatible changes, I suggest that we say we don't provide --pyversion option any more and simply compile 2.5 compatible interpreter. I don't really see benefits of providing 2.4 right now (after a brief discussion with Armin). If anyone objects, please do that now. Cheers, fijal