MacOS port functional too (was Re: [multi-tty] Emacs port status)

[Dan Nicolaescu]

The MacOS port is functional now. 
When compiling for X11 all the multi-tty functionality that is
available on other platform works as well. 

When compiling for the native Carbon toolkit it is possible to use
both terminal and Carbon frames simultaneously. 

Everything was only very lightly test as I run out of time, I have
done this work on a borrowed machine that I had to return. I am not
sure that I am going to have access to such a machine any time soon. 
(This is the first time ever that I compiled _any_ code on a Mac...)

Please take multi-tty for a spin on a Mac.