[CM] still have problem with xcmnw

[Bill Schottstaedt]

>   n = read(*fd,buffer,4);
>    if (0 == n)
>          exit(0);

Thanks! I'll merge this into my version (and maybe prettify that
code finally -- it was written in "type-as-fast-as-you-can" mode) --
I think my intention was to call cmn-pclose
in an exit method -- can't remember off the top of my head
whether one is available in cmucl.

There's also a commented-out block of code in cmn-all.lisp that
builds xcmnw when cmn is built -- I think it needs to check that
X/Motif are available, then fixup the various -I and -L values --
if I can find time, I'll look into running configure instead --
lisp itself doesn't need to know what's going on in this case.