BooleanQuery rewrite optimizations

A couple of BooleanQuery rewrites / optimizations.

First, as discussed on the user group, a BooleanQuery with a query that is both a SHOULD and a FILTER can be rewritten as a single MUST query, but care must be taken to decrement minShouldMatch by 1.

Another case is if a query is both required (MUST or FILTER) and MUST_NOT at the same time, it can be converted to a MatchNoDocsQuery (although I haven't discussed this yet so hopefully I'm not missing something!).