TableColumnExt not respecting prototype value
===

I'm trying to use SwingX's `TableColumnExt` class to set a prototype value for the column's width in the hierarchical column of a `JXTreeTable`. After I initialize the model and table I do this:

`
    TableColumnExt column = dataTable.getColumnExt(0);            
    column.setPrototypeValue(500);
`

When my table is rendered, all columns are equally sized. These are the methods I'm using on the `JXTreeTable` instance.

`
    dataTable.setRowHeight(28);
    dataTable.setFillsViewportHeight(true);
    dataTable.setHorizontalScrollEnabled(true);
`

What am I doing wrong here?
