Added filter support in the `has_child` and `has_parent` filters.

Example:
```
curl -XPOST 'localhost:9200/_search' -d '{
  "query": {
    "filtered_query": {
      "query": {
        "match": {
          "title": "distributed systems"
        }
      },
      "filter": {
        "has_child": {
          "type": "tag",
          "filter": {
            "term": {
              "name": "book"
            }
          }
        }
      }
    }
  }
}'
```

Closes #2588

Conflicts:
	src/main/java/org/elasticsearch/index/query/HasChildFilterParser.java
	src/main/java/org/elasticsearch/index/query/HasParentFilterParser.java