Query DSL: Allow to set boost on has_child query, closes elastic#884.

Author: kimchy

modules/elasticsearch/src/main/java/org/elasticsearch/index/query/xcontent/HasChildQueryParser.java

@@ -73,6 +73,8 @@ public class HasChildQueryParser extends AbstractIndexComponent implements XCont
  childType = parser.text();
  } else if ("_scope".equals(currentFieldName)) {
  scope = parser.text();
+ } else if ("boost".equals(currentFieldName)) {
+ boost = parser.floatValue();
  }
  }
  }