[CM] s7_string v. s7_object_to_c_string

[bil at ccrma.Stanford.EDU]

No it is not a bug.  s7_string returns the bytes of the
scheme string (which is not a C string), somewhat like
display, whereas s7_object_to_c_string returns a human-
readable representation of a scheme object, somewhat like
write:

<1> (format #f "~A" "asdf")  ; display
"asdf"
<2> (format #f "~S" "asdf")  ; write
"\"asdf\""