Fix issue with multi-field values #302

The difference between

```
=> select * from cdb_service_quota_info();
    service     | monthly_quota | used_quota | soft_limit |     provider
----------------+---------------+------------+------------+------------------
 isolines       |          1000 |          0 | f          | heremaps
 hires_geocoder |             5 |          2 | f          | mapzen
 routing        |       1500000 |          0 | f          | mapzen
 observatory    |          1000 |          0 | f          | data observatory
(4 rows)
```

and

```
=> select cdb_service_quota_info();
          cdb_service_quota_info
-------------------------------------------
 (isolines,1000,0,f,heremaps)
 (hires_geocoder,5,2,f,mapzen)
 (routing,1500000,0,f,mapzen)
 (observatory,1000,0,f,"data observatory")
(4 rows)
```

is important to pl/proxy. In the later case, rows only have one field
(a tuple) and it complains with "Got too few fields from remote end".

client/renderer/interface.yaml

@@ -380,6 +380,7 @@
 - name: cdb_service_quota_info
   return_type: SETOF cdb_dataservices_client.service_quota_info
   multi_row: true
+  multi_field: true
   params:
     - {}