How do we handle bootstraps under the MCConfiguration technology?

[Daniel Vainsencher]

As often happens, the Traits upgrade requires a process, it is not 
sufficient to just load the post-Traits versions of the the image packages.

What it will require, is for the image being upgraded, to load a 
specific sequence of versions, which slowly and safely bring it into the 
desired state.

Exactly the same thing is required for other things, such as fixing the 
awful performance bug in Set+Behavior that causes a Set with 7000 
classes to use almost exclusively linear search. This would require 
loading a version of the scanFor: that tries two different ways to use 
the hash, preferring the more efficient one, but tolerating the old one 
(that all Sets happen to be using at the moment), then doing rehash on 
all Sets, then dumping the old hashing code.

So this is a general problem. Does the current update stream mechanism 
allow us to give the user a sequence of MCConfigs, instead of just the 
one config that has the appropriate delta?

Daniel