"unsubscribed" event is never triggered (with fix)

I'm using WebSocket as the socket mechanism and when the server unexpectedly drops the connection, the "unsubscribed" event is never emitted due to the bug in the following 2 lines:

``` js
this.subscribed = false;
if (this.subscribed) this.emit('unsubscribed'); // never triggered!!
```

located in lib/client/doc.js:407

Here is my fix:

``` js
var wasSubscribed = this.subscribed;
this.subscribed = false;
if (wasSubscribed) this.emit('unsubscribed');
```