void ProjectIconCellDataFunc(CellLayout layout, CellRenderer cell, TreeModel model, TreeIter iter)
{
CellRendererPixbuf cpix = cell as CellRendererPixbuf;
var item = (Project)model.GetValue (iter, 0);
if (cpix == null || item == null)
return;
if (item.Id == -1) // Inbox
cpix.StockId = "adroit-inbox";
else if (item.Id == -2) // Reference
cpix.StockId = "adroit-reference";
else if (item.Id == -3) // Incubator
cpix.StockId = "adroit-incubator";
else
cpix.StockId = Stock.Directory;
}