[CM] Port output function receives string 1 char at a time

[bil at ccrma.Stanford.EDU]

Thanks for the suggested code, but that is not how
I want to do it, if I do it at all.  This is a minor
optimization, so it should not introduce compile-time
switches that split s7 into two incompatible versions;
I'd have to add stuff to ffitest.c and the documentation
and so on.  I'll look at it later.