Catch NotFound error in resource_proxy

```
Stacktrace (most recent call last):

  File "raven/middleware.py", line 35, in __call__
    iterable = self.application(environ, start_response)
  File "ckan/config/middleware.py", line 373, in __call__
    return self.app(environ, start_response)
  File "/usr/lib/ckan/demo/lib/python2.7/site-packages/paste/cascade.py", line 130, in __call__
    return self.apps[-1](environ, start_response)
  File "ckan/config/middleware.py", line 238, in __call__
    return self.app(environ, start_response)
  File "/usr/lib/ckan/demo/lib/python2.7/site-packages/paste/registry.py", line 379, in __call__
    app_iter = self.application(environ, start_response)
  File "/usr/lib/ckan/demo/lib/python2.7/site-packages/repoze/who/middleware.py", line 107, in __call__
    app_iter = app(environ, wrapper.wrap_start_response)
  File "webob/dec.py", line 147, in __call__
    resp = self.call_func(req, *args, **self.kwargs)
  File "webob/dec.py", line 208, in call_func
    return self.func(req, *args, **kwargs)
  File "fanstatic/publisher.py", line 234, in __call__
    return request.get_response(self.app)
  File "webob/request.py", line 1053, in get_response
    application, catch_exc_info=False)
  File "webob/request.py", line 1022, in call_application
    app_iter = application(self.environ, start_response)
  File "webob/dec.py", line 147, in __call__
    resp = self.call_func(req, *args, **self.kwargs)
  File "webob/dec.py", line 208, in call_func
    return self.func(req, *args, **kwargs)
  File "fanstatic/injector.py", line 54, in __call__
    response = request.get_response(self.app)
  File "webob/request.py", line 1053, in get_response
    application, catch_exc_info=False)
  File "webob/request.py", line 1022, in call_application
    app_iter = application(self.environ, start_response)
  File "beaker/middleware.py", line 73, in __call__
    return self.app(environ, start_response)
  File "beaker/middleware.py", line 155, in __call__
    return self.wrap_app(environ, session_start_response)
  File "routes/middleware.py", line 131, in __call__
    response = self.app(environ, start_response)
  File "pylons/wsgiapp.py", line 125, in __call__
    response = self.dispatch(controller, environ, start_response)
  File "pylons/wsgiapp.py", line 324, in dispatch
    return controller(environ, start_response)
  File "ckan/lib/base.py", line 346, in __call__
    res = WSGIController.__call__(self, environ, start_response)
  File "pylons/controllers/core.py", line 221, in __call__
    response = self._dispatch_call()
  File "pylons/controllers/core.py", line 172, in _dispatch_call
    response = self._inspect_call(func)
  File "pylons/controllers/core.py", line 107, in _inspect_call
    result = self._perform_call(func, args)
  File "usr/lib/ckan/demo/src/ckan/ckanext/resourceproxy/controller.py", line 78, in proxy_resource
    return proxy_resource(context, data_dict)
  File "usr/lib/ckan/demo/src/ckan/ckanext/resourceproxy/controller.py", line 23, in proxy_resource
    resource = logic.get_action('resource_show')(context, {'id': resource_id})
  File "ckan/logic/__init__.py", line 419, in wrapped
    result = _action(context, data_dict, **kw)
  File "ckan/logic/action/get.py", line 899, in resource_show
    raise NotFound
```