Add an operator to query parser for term quorum (ie: BooleanQuery.setMinimumNumberShouldMatch) [LUCENE-3833]

A project I'm working on requires **term quorum** searching with stemming turned off. The users are accostomed to Sphinx search, and thus expect a query like [ A AND (B C D)/2 ] to return only documents that contain A or at least two of B, C or D.

So this document would match:
a b c

But this one wouldn't:
a b

This can be a useful form of fuzzy searching, and I think we support it via the MM parameter, but we lack a user-facing operator for this. It would be great to add it.

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Migrated from [LUCENE-3833](https://issues.apache.org/jira/browse/LUCENE-3833) by Mike Lissner (@mlissner), 1 vote, updated Oct 27 2012
Attachments: [LUCENE-3833.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-3833/LUCENE-3833.patch)
Linked issues:
- [SOLR-2368](https://issues.apache.org/jira/browse/SOLR-2368)
- [SOLR-3028](https://issues.apache.org/jira/browse/SOLR-3028)

Start by tracing the query parser's handling of Boolean expressions and the existing MM parameter; the issue's A AND (B C D)/2 example defines the expected semantics. Review the attached LUCENE-3833.patch for historical context. Done means the parser accepts a term-quorum operator and produces the described minimum-should-match behavior.

Written by the indexing model from the issue text.