feat(stream watchers) disable double chunking

Both golang http client and curl command does auto dechunking so I have to test it with telnet. Here is a sample output after this commit:

```
cenk@tardis ~ (master) $ telnet 127.0.0.1 4001
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET /v2/keys/a?wait=true&stream=true HTTP/1.1

HTTP/1.1 200 OK
Content-Type: application/json
X-Etcd-Index: 1203
X-Raft-Index: 9698
X-Raft-Term: 4
Date: Fri, 10 Jan 2014 13:08:26 GMT
Transfer-Encoding: chunked

a6
{"action":"set","node":{"key":"/a","value":"3","modifiedIndex":1204,"createdIndex":1204},"prevNode":{"key":"/a","value":"1","modifiedIndex":1203,"createdIndex":1203}}
a6
{"action":"set","node":{"key":"/a","value":"4","modifiedIndex":1205,"createdIndex":1205},"prevNode":{"key":"/a","value":"3","modifiedIndex":1204,"createdIndex":1204}}
^]
telnet> q
Connection closed.
```