[vos-d] Movement interpolation update

[Reed Hedges]

Karsten Otto wrote:
> You cannot really fix this with a "don't-interpolate" flag,  
> as there is no good place to put one. You could extend the property- 
> update notification, but a lot of properties do not use interpolation  

That's ok. Nothing stops you from adding whatever fields you want to the 
message, and for Terangreal to check for the field for the position 
property. This is why fields have names.

Pete's idea of having extensible method types is interesting though, 
might be useful.

Reed