Bulk update doesn't support fields parameter

[clintongormley]

The fields parameter in the update API allows the user to retrieve the updated _source field. This support is missing in the bulk update API:

PUT test/test/1
{
  "foo": 1
}

POST /test/test/1/_update?fields=_source
{
  "doc": {
    "foo": 2
  }
}

Neither the QS param nor in the body return the _source field:

POST /test/test/_bulk?fields=_source
{"update": { "_id": 1}}
{"fields": ["_source"], "doc": {"foo": 3}}

And throws an exception if specified in the metadata line:

POST /test/test/_bulk
{"update": { "_id": 1, "fields": "_source"}}
{"doc": {"foo": 3}}