[CM] mouse-drag-hook in FTH?

[Bill Schottstaedt]

mouse-drag-hook is called only if you drag the mouse in
the "lisp graph" -- a confusing name now that it isn't
specific to scheme -- that's the 3rd graph on the right
(if you're doing your own displays or envelope handlers).
You can get the same effect if you have either xg or xm
loaded by adding your own callback function for that
on the graph widget (I'm actually guessing here, but
it seems unproblematic).