Hello all,

I've attached a preliminary implementation of MVars à la Concurrent
Haskell for Guile.  I made a few small changes to the API to better
match Scheme conventions, and added atomicity guarantees for 'read-mvar'
and 'swap-mvar'.  I also added the interface 'try-read-mvar'.

Note that the fairness of this implementation relies upon the fairness
of Guile's mutexes and condition variables, which I have not checked.

Comments and suggestions welcome.

I was thinking that maybe we should add something like this to core
Guile.  What do you think?

     Mark