[Mono-list] New io library

[Dick Porter]

I've just checked in the first part of a new IO library for mono, in the
mono/io-layer directory.  It's designed to emulate the win32 threading
and IO API for Linux and Linux-like systems, but use the win32 calls for
native Windows and Cygwin builds.  Cygwin users will need the w32api
package that is distributed with Cygwin.  I don't know if anyone
actually builds Mono under native Windows yet, but this work should make
it possible.

The win32 API was chosen for this because it (for obvious reasons)
closely matches the .NET model.

The library builds for me under both Linux and Cygwin, but it isn't
actually used in the rest of the Mono code yet.  That is the next task. 
For now, if the build fails in the io-layer directory you can comment
that part out in the Makefile, but _please_ tell me (or even better,
send me a patch to fix the problem.)

- Dick