Flash MultiScaleContainer bug (and fix)

There seems to be a bug in org.openzoom.flash.components.MultiScaleContainer, in dispose(). Lines 823 and 824 call super.numChildren/super.removeChildAt(). As a result, the override of removeChildAt() is not called. Perhaps there's a reason for this but it looks like a bug and results in invalid objects hanging around. Removing super doesn't seem to have any adverse affects.