Strengthen the function of Min should match, making it select BooleanClause as Occur.MUST according to the weight of query

In current version, when we using BooleanQuery do disjunction, the top scorer will select the doc which meet
at least mm numbers of sub scorers.

But in some case, we wish that the weight of sub scorers larger than the threshold can be selected
as Occur.MUST automatically. The threshold can be configurable, equaling the minimum integer by default.

Any comments is welcomed.