[CM] Examples of printing out errors in S7?

[bil at ccrma.Stanford.EDU]

> What is the reason we need to do the gc_protect and later unprotect of 
> the old port?

It looks like I never addressed that in s7.html.  There is a short
explanation in s7.h under s7_gc_protect.  In s7, the GC can run
at any time.  If you have stored a reference to an s7 object,
and the GC might run during its lifetime, and its lifetime
is not really short (there's a lag between the making of an object
and its first possible GC), you need to protect it.  It will remain
protected until you unprotect it, so to avoid an ever-growing heap,
you need to unprotect it.