[CM] length of output_string

[Woody Douglass]

All,

Does it make sense to have s7_get_output_string also return the length
of the string? i'm working on a program that does some binary IO, and
there are some 0s in my stream...

so the new signature would be
const char *s7_get_output_string(s7_scheme *sc, s7_pointer out_port,
size_t *len);

if the signature needs to remain compatible, i could make that last
argument variadic, and then just document the behavior...

Thanks,
Woody Douglass