Support class-specific callbacks

From: http://usejsdoc.org/tags-callback.html#examples
```js
/**
* @class
*/
function Requester() {}

/**
* Send a request.
* @param {Requester~requestCallback} cb - The callback that handles the response.
*/
Requester.prototype.send = function(cb) {
// code
};

/**
* This callback is displayed as part of the Requester class.
* @callback Requester~requestCallback
* @param {number} responseCode
* @param {string} responseMessage
*/
```

The above code results in the error: `Unexpected token, expected , `. Removing the `Requester~` prefix seems to make things happy, but then the callback is documented globally.

Start with the JSDoc example in the issue and reproduce the `Unexpected token, expected ,` error using the `Requester~requestCallback` reference. Compare it with the unprefixed callback case; the work is done when class-specific callbacks parse successfully and remain documented as part of `Requester` rather than globally.

Written by the indexing model from the issue text.