[R6RS] incomplete draft of revised i/o

[R. Kent Dybvig]

I agree with Will that the magical mystery procedure should be eliminated. 
I would go further and change the interface to string and bytevector
ports, i.e., have the string and bytevector output port creation routines
return two values:  a port and a procedure.  The procedure would be used
to get the output.  This interface would be just as easy to use in all of
the code I have that uses string output ports, it reduces the complexity
and number of procedures in the report, and it can be implemented without
the magical mystery procedure.

Kent