Removal of Scorer.weight

I've been playing with reducing the dependency between BooleanWeight, BooleanScorer, and BooleanScorer2. Instead of letting the scorers generate their coord factors, now BooleanWeight generates them in one place for all the scorers that it instantiates. After seeing how smoothly that went, I decided to try and push it forward a little by removing Scorer.weight and the need to pass in a weight (or null) to Scorer's constructor.

The tests green bar with `tests.disableHdfs=true` and `tests.slow=false`.

What do you guys think? I'm happy to adjust and port to trunk if you are interested.

--Terry