Cache no longer works (angular >= 1.3)

Hey all,

Because of this line from Angular 1.2:

``` javascript
return fn.apply(self, args);
```

https://github.com/angular/angular.js/blob/g3_v1_2/src/ng/parse.js#L595

Was changed to this line in Angular 1.3:

``` javascript
return fn.apply(undefined, args);
```

https://github.com/angular/angular.js/blob/g3_v1_3/src/ng/parse.js#L568

`this` in all the filters is no longer linked to the scope that called the filter and therefor **filterWatcher** gets `scope=undefined` which causes `isScope(scope)` to always return `false` which in turn causes `cleanStateless()` to get called after every filter call, `cleanStateless()` cleans the cache.

The consequence is major performance issues and slowdown on every $digest cycle (which re-evaluates the filter output even though the input did not change).