Can not use filters on datastore_search on a GET request

The JSON object does not get decoded and returns an error:

http://beta.ckan.org/api/action/datastore_search?resource_id=50f6abfc-1ff3-4885-8d8b-ec452605f159&filters={%22Unit_Type%22:%22District%22,%22Prov_Name%22:%22Farah%22}

```
{"success": false, "error": {"__type": "Validation Error", "filters": ["Not a json object"]}}
```