[plt-scheme] Suggestion for (lib "date.ss"): add timezone to 'american

I start at the US Naval Observatory for information regarding clocks  
and time.
This has all the single-letter world time zone abbreviations (e.g.,  
Z=Zulu=GMT=UTC):

   http://aa.usno.navy.mil/faq/docs/world_tzones.php

I've seen -0700 written as UTC-0700 and GMT-0700.

This list of commonly used abbreviations looks decent:

   http://www.timeanddate.com/library/abbreviations/timezones/

but there are more...

   http://wwp.greenwichmeantime.com/time-zone/time-zones.htm
   http://www.timegenie.com/timezones.php
   http://www.worldtimezone.com/wtz-names/timezonenames.html

On my computer, there's some interesting time zone info in my  
PostgreSQL installation:

   /opt/local/share/postgresql82/timezonesets  (readable ASCII)

But the pièce de résistance, gobs of time zone info for hackers:

   http://www.twinsun.com/tz/tz-link.htm

Happy Thanksgiving everyone!

Geoffrey