Vague error message when trying to create a volume size that exceeds quota

Horizon displays a confusing error message if a user tries to create a volume that exceeds the quota for volume size:

"Error: Error Creating Volume: The server has either erred or is incapable of performing the requested operation."

The underlying exception is a QuotaError which should be handled explicitly. Full logs:

2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/request.py", line 1053, in get_response
2012-06-13 21:58:48 TRACE nova.api.openstack application, catch_exc_info=False)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/request.py", line 1022, in call_application
2012-06-13 21:58:48 TRACE nova.api.openstack app_iter = application(self.environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/keystone/middleware/auth_token.py", line 176, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack return self.app(env, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack return resp(environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack return resp(environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack return resp(environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/pymodules/python2.7/routes/middleware.py", line 131, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack response = self.app(environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack return resp(environ, start_response)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 147, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack resp = self.call_func(req, *args, **self.kwargs)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 208, in call_func
2012-06-13 21:58:48 TRACE nova.api.openstack return self.func(req, *args, **kwargs)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/nova/api/openstack/wsgi.py", line 803, in __call__
2012-06-13 21:58:48 TRACE nova.api.openstack content_type, body, accept)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/nova/api/openstack/wsgi.py", line 851, in _process_stack
2012-06-13 21:58:48 TRACE nova.api.openstack action_result = self.dispatch(meth, request, action_args)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/nova/api/openstack/wsgi.py", line 926, in dispatch
2012-06-13 21:58:48 TRACE nova.api.openstack return method(req=request, **action_args)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/nova/api/openstack/volume/volumes.py", line 249, in create
2012-06-13 21:58:48 TRACE nova.api.openstack **kwargs)
2012-06-13 21:58:48 TRACE nova.api.openstack File "/usr/lib/python2.7/dist-packages/nova/volume/api.py", line 87, in create
2012-06-13 21:58:48 TRACE nova.api.openstack raise exception.QuotaError(code="VolumeSizeTooLarge")
2012-06-13 21:58:48 TRACE nova.api.openstack QuotaError: Quota exceeded: code=VolumeSizeTooLarge