mbostock/d3 — pull request #596 by jasondavies (2012-03-19 20:25:40+00:00)
Title: Sorting NaNs with d3.{ascending,descending}.

Previously, this was happening:

```javascript
[1, 5, NaN, 3, 2].sort(d3.ascending);
[1, 5, NaN, 2, 3]
```

Native sort ignores undefined values, so sorting [1, 5, undefined, 2, 3] worked as expected, but this change fixes d3.ascending and d3.descending for any orderable value, including undefined.