ignore_missing removed from _aliases
Continuing discussion from:
https://github.com/elasticsearch/elasticsearch/pull/7234#issuecomment-55948380

It appears that the recent Get Indices API removes ignore_missing:

Elasticsearch 1.3.2

```
curl -XGET  http://localhost:9200/logstash-2014.09.16,logstash-2014.09.17/_aliases?ignore_missing=true;echo
{"logstash-2014.09.16":{"aliases":{}}}
```

Elasticsearch 1.4 branch

```
$ curl -XGET  http://localhost:9200/logstash-2014.09.16,logstash-2014.09.17/_aliases?ignore_missing=true;echo
{"error":"IndexMissingException[[logstash-2014.09.17] missing]","status":404}
```

Technically ignore_missing was slated for removal in Elasticsearch 1.0 (http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/_parameters.html#_parameters), however it was not removed from this API, meaning this this will introduce a breaking change for 1.4. 

It might be better to deprecate ignore_missing and remove it in Elasticsearch 2.0.
