Unable to create directories

According to https://github.com/coreos/etcd/blob/master/Documentation/api.md#creating-directories, the following example should create a directory:

```
% curl -L http://127.0.0.1:4001/v2/keys/dir -XPUT -d dir=true
{"action":"set","node":{"key":"/dir","value":"","modifiedIndex":71,"createdIndex":71}}
```

Note the lack of `"dir": true` in the returned object. Thinking that maybe the `dir` key is just missing, I tried to create a key under the `/dir` keyspace:

```
% curl -L http://127.0.0.1:4001/v2/keys/dir/key -XPUT -d value=foo
{"errorCode":104,"message":"Not a directory","cause":"/dir","index":71}
```
added