skipTo seems to be optional functionality on the Scorer class (BooleanScorer
doesn't implement it). BooleanQuery.scorer() tests all subclauses using
"instanceof BooleanQuery" to determine if it can use a ConjunctionScorer that
requires skipTo functionality.
This means that any other new Query/Scorer that don't implement skipTo will get
into trouble when included in a BooleanQuery.
If skipTo is really optional, then there should be some way of telling by the
Scorer or the Query in a more generic manner.
1) have a "boolean Scorer.hasSkipTo()" method
2) have a "boolean Query.hasSkipTo()" method
3) remove Scorer.skipTo and have a "public interface ScorerSkipTo
" that scorers may implement