Container attaching from @ukd1, @diffoperator, etc.

I decided to place this in a separate branch and not merge to master until the upstream Docker has merged the dotcloud/docker#1146 pull request.  Thanks to the tremendous work from @ukd1, @diffoperator, and their team for adding this.  Below are the steps to get this working from the 1146 PR.

Clone the latest Docker and checkout the latest stable tag (currently v0.4.8):

```
git clone https://github.com/dotcloud/docker.git
```

```
git checkout v0.4.8
```

Add the upstream from the pull request dotcloud/docker#1146:

```
git remote add ws https://github.com/benoitc/docker.git
```

Create a websocket branch (optional):

```
git checkout -b websockets
```

Merge code from pull request:

```
git pull ws feature/attach_ws
```

Build new Docker binary:

```
make
```

Now you can run `bin/docker` and use Shipyard (terminal branch) to access the console via websockets.