[Rearranger] Tree doesn't autoscroll

Hey Dave,

if I have a class that has enough fields and methods
to make the tree longer than the Live Rearranger dialog,
then if I move my cursor down the tree past the bottom
of the dialog when moving things (with Ctrl-Shift-Down)
then the cursor disappears (i.e. the dialog should scroll the
tree automatically to keep the cursor always visible).

The behavior is correct when just moving along the tree
with up/down though.

Thanks,

Vince.