Bug when querying numeric(-al) values

When querying numeric values

```
TypeError: Cannot read property 'length' of undefined
    at Array.dv.table.table.dense_query (http://127.0.0.1:9000/lib/datavore/dv.js:150:32)
```

which is the following line

```
    sz.push(col.lut.length);
```

Root cause is probably due to the fact that numeric col doesn't have lut table. 
