How to make selected row visible in GTK TreeView?

[Chris Green]

I have a GTK TreeView with scrollbars which enables me to scroll
through the values OK.  Clicking on a row selects it and highlights
it. 

However if one uses 'down arrow' to move the selection/highlight down
the list then the selected row disappears from the visibble window.
How can I scroll the window so that the selected row remains visible? 

I would also like a 'go to row x' function to scroll to a specific
row in the list and highlight it.  I guess this would need very
similar code to the first requirement.

-- 
Chris Green
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