misleading error trying to select from non-existent series

```
graphite> select * from this-series-DEFINITELY-doesnt-exist
graphite> ✘ Error: Couldn't look up columns for series: this-series-DEFINITELY-doesnt-exist
```

error should be something like "series 'this-series-DEFINITELY-doesnt-exist' not found"

<!---
@huboard:{"order":743.0,"milestone_order":778,"custom_state":""}
-->