Make available timing distribution curve

```
Perhaps this is already possible with Kevin's redesign, but I'll write it here
to check.

I need to report 99th or 99.9th percentile (etc) timings for latency
measurements where mean and stdev is helpful but worst case is also very
important. Doesn't need to be "out of the box", just possible.
```

Original issue reported on code.google.com by `brianfromoregon` on 20 Apr 2011 at 12:53