Parallel coordinates plot
A couple of comments and I'm going to make some quick edits.
- Best way to check for None is `obj is None` instead of `obj == None`. The latter will fail on many values of `obj`
- The fastest way to get the values in a row of a DataFrame is to use `irow`, `xs`, or indexing with `ix`. This function has issues with integer indexes (http://pandas.pydata.org/pandas-docs/stable/whatsnew.html#api-changes-to-integer-indexing) that I'm fixing now
 Also here's a more pandas-ian way for the following few lines:

``` python
    if cols is None:
        columns = data.drop(class_column, axis=1)
    else:
        columns = data[cols]
```

instead of 

```
    if cols is None:
        columns = [data[col] for col in data.columns if (col != class_column)]
    else:
        columns = data[cols] [data[col] for col in cols]
```
 I see. This pattern is also in most other of my multi-variate data visualization routines.
