moses: boosting: scoring must always be relative to best-possible score.
Remove dead code.
moses: remove more dead code, fix documentation
moses: boosting: Add handling for the best-possible score.
moses:boosting: cleanup of perfectly-scored tree.
moses: ctable scores now relative to the best-possible scores.
moses: re-instate some missing initializations
moses: boosting: re-enable unit tests

With this, we've made up all of the lost ground. Phew.