S9 LIB  (append-to-output-file string)  ==>  output-port

Take a string naming an output file and return an output port
capable of writing characters to the that file. Characters
written to the port will be appended to the file. When the
file does not exist when this procedure is called, it will
be created. If the file cannot be opened, an error is signalled.

(append-to-output-file "logfile")  ==>  #<output-port>
