Here's a patch for adding SRFI-123 support.  It applies on stable-2.0.

Please tell me if the changes to (srfi srfi-9) and (rnrs bytevectors)
are OK.  The test suite passes.  I also added a rudimentary test-suite
for SRFI-123.

I kept the documentation brief, since the full documentation can be
found in the SRFI document itself.


To clarify: this SRFI caters to programmers writing code that is 1) not
performance-critical, 2) rich in calls to verbose procedures like
hashtable-ref which become annoying.  "Scripty" code if you will.  It's
also a matter of taste.  It doesn't have much foot-shooting potential so
having it shouldn't hurt.  (Making this disclaimer because some Guilers
didn't seem to like it.)


Thanks in advance for the review. :-)
Taylan