PHP-1259: MongoDB::listCollections() should support filter option

https://jira.mongodb.org/browse/PHP-1259
After extracting `includeSystemCollections`, `$options` is passed directly to the server. I didn't see the point of validating options when we don't need to (that's gotten us into trouble before). I would expect the server to raise an error and have the command fail, but that wouldn't be our exception.

The only reason we check "filter" here is because we need to extract it from `$options` and use it to construct a cursor, which requires an array/object type.