[CM] fn defined in C returns to wrong place

[bil at ccrma.Stanford.EDU]

I think where you call s7_read, you want to wrap that
in a catch, probably using s7_call_with_catch.  There
are examples of it in ffitest.c.  The only tricky part
(I hope) is passing the "port" argument into the
thing called by the catch -- the catch "body" function
takes no arguments, as in scheme.