[Dev] Avoiding unnecessary rendering.

[John Anderson]

Hi Bryan:

I've been working on Bug #4009. For starters I'm trying to avoid 
unnecessary rendering and unrendering. So when a tree of blocks is 
rendered and its contents change, instead of unrendering and rerendering 
I now just sent a SetContents event. Trees need to handle this buy 
updating themselves as appropriate when they are already rendered. This 
seems to work everywhere except the detail view. So I've assigned the 
bug to you for your opinion on how practical this is in the detail view 
case. Once we resolve this assign it back to me.

John