Scroll Model Range

Team,

I would like to propose a modification to scroll_model.  Right now you
can scroll as far to either side as you want.  IMO this is wrong.

I propose the following constraints:

end - size >= start >= 0

This is just for the model itself.  If you want to be able to scroll
passed whatever is in the container the model represents, just increase
the model size.


Any objections (with reasons) ?

Darren