Allow _id to be filtered on, even when not_indexed

[jimmyjones2]

Because _id is not indexed, it's not possible to filter on it in the Kibana 4 Discover page. However _id is a special case and can be filtered - http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-id-field.html

Having said that, not sure how useful the ability to filter on _id is...

[rashidkpc]

An excellent point. We could put in a special check to force _id to appear as indexed. Alternatively you can simply index the _id field in the meantime.