Co-Routines in CLI

Paul expressed concerns whether real co-routines are possible or not in the
.net interpreter CLI.  I think I found an existence proof.  I found a paper
from Micosoft about a language called Polyphony that is C# with co-routines
added to it:

http://research.microsoft.com/Users/luca/Papers/Polyphony%20ECOOP.A4.pdf

It has a strange concurrency model that is half-way to a "channel" but
shows how to implement a real channel using their language.  I also shows
how the polyphony compiler would implement the concurrency features using
the existing thread primitives in the CLI environment.  It discusses
perfomances issues in depth.  It also discusses light-weight threads but
I'm not sure if they can be implemented.

I have just skimmed the paper so far. Now I'm going back and reading it in
detail.

The good news is that I think it answers the question of whether
co-routines can be implemented in CLI in the affirmative.