The has_filter method should also take the $exclude parameter (or NULL)?

Right now the has_filter method of the query class does not have an option to match the #exclude parameter of a filter, which seems like an API failure. This would be especially helpful for facet queries.

I propose that we add a 3rd param with a default NULL value. The behavior in the case of NULL would be like now - it matches either value of #exclude, but if it's set it would only return true if that value matches as well.