PATCH: Treeview and arrow key navigation

Hi,

Find attached patch for making arrow keys usable on non-windows(Ubuntu in my case) platform.
this patch will work in this way
 ---> key :- If item has no child , not effect.If it has children, and is not expanded. This key will expand it. If it
haschildren and already expanded, go to first child. 

<--- key :- If item has no child, go to parent item. If it has children and expanded , collapse it. If it has children
andalready collapsed, go to parent item. 

Remaining two keys are working as they should be.

regards,
Prasad Somwanshi