Flow integration

(This is a draft I think we should post to the squeak-dev to generate
the main discussion there. If you guys have comments/additional issues
to raise...)

As I noted before, a few people have requested that the Flow work by
Craig be integrated into the base image.

This work:
 - Replaces the primitive interface to sockets and other External
Resources
 - Refactors the stream hierarchy

I've had a few concerns that the changes might create too much change
all at once, considering that many things use the stream hierarchy.
After speaking to Craig about these issue, it seems that (Craig, please
correct me if I'm wrong here)-
1. The new streams implement all the old protocols, so that the main
compatibility problem should be direct references to the old class
names. This is easy to fix incrementally for packages, and fairly
quickly for the image itself.
2. The package as it is now can coexist with the existing libraries,
making testing quite feasible at low risk.

So I guess this move should be pretty easy. Open questions -
1. Should we do it?
2. How do we test to minimize risk?
3. When?

1. Do or not?
If people know of any general objections/problems with this code, it's
best to put them in the open now.

I'm not qualified to answer about the benefits of the new primitive
interfaces, I'm quite ignorant in these things. John M has (IIUC) spoken
in favor of it. Could we get some more input from the experts?

About the stream refactorings, I think several people have used Flow to
develop their own applications. Luciano has mentioned that he's used it
for several and liked it. More evaluations would be useful here.

2. Testing
As to format, Craig has agreed to post these changes on SM in the
precise form he'd prefer to issue the proposed updates. As to how to
make sure it doesn't cause problems for this or that package or
application - that's up to you guys out there that use your sockets for
more than reading mail... ideas?

3. When?
Probably not in 3.4 (just to keep the release finite and near), but
possibly in 3.5. This depends on Craig posting on SM in the proposed
format, and mostly on when we get enough testing input.

Daniel