[CM] Access SND from CLM

[Bill Schottstaedt]

I checked the clm/snd business, and think I guessed right for once --
I added a warning, so that you'll get some indication when the
connection fails.  The communication between snd and clm is
handled by X window properties (earlier attempts to use pipes
and temporary files were a disaster), so both clm and snd have
to be able to open an X11 display.  There must be a way to
do the same thing in Apple's OS, but I don't know what it is.
By the way, thanks for the tip about open-x11 -- I'll add that
to the snd documentation.