[PD] support for scrollwheel in patchers

[Mathieu Bouchard]

in u_main.tk (pd.tk), at the end of proc pdtk_canvas_new, add this:

   bind $name.c <Button-4> "$name.c yview scroll -1 units"
   bind $name.c <Button-5> "$name.c yview scroll +1 units"

This enables the mouse wheel in patchers. Of course I will later provide a
means to reconfigure it to do something else depending on what is most
useful to a given user. (Some would like numberboxes to be scrollenabled,
but that's conflicting with the above setting, so i'd give an option)

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Mathieu Bouchard                       http://artengine.ca/matju