lowercase get method in mget causes failed to derive from xcontent

The following call doesn't work from sense because of the lowercase get, although with other apis that (GET vs get) doesn't seem to be a problem:

```
get _mget
{
"docs" : [
{
"_index":"my_index",
"_type":"my_type",
"_id":"1"
}
]
}
```

causes a "failed to derive from xcontent error returned from elasticsearch, I guess because of the incorrect request body that gets sent.

Following call works perfectly though:

```
GET _mget
{
"docs" : [
{
"_index":"my_index",
"_type":"my_type",
"_id":"1"
}
]
}
```