Table: Additional spatial lags

```
(from Sep 9, 2009)
additional spatial lags: not just average but also sum and conditional sum,
in case people want totals or want to compute rates or lagged rates (as
requested by jkoschinsky).

This could be part of the table refactoring. May be it makes sense to do one
ticket: Refactor Table and then put all the small table enhancements in as
subsets?
```

Original issue reported on code.google.com by `mmcc...@gmail.com` on 5 Mar 2013 at 5:27