[CM] s7: Legality of calling s7_error from C (without being called from scheme)

[bil at ccrma.Stanford.EDU]

s7_error will look for an active (s7-internal)
setjmp if the error
is not otherwise caught, and not handled by *error-hook*;
if it doesn't find one, it just returns.  In the
code you sent, I think it just returns after
trying to print the error info.

I think Snd sets up its own top-level setjmp
and catches this case so that uncaught errors
always return to its top level.