Adjust commentary to try to defuse recent issues somewhat.

This change stemmed from a long discussion on the tz mailing list
about what country the Jerusalem zone entry is in.  The idea of
this change is to deemphasize the role of countries in the tz
database, to lessen the amount of controversy in the future.
Due to backward compatibility concerns this change does not eliminate
the role of countries entirely.  With one minor exception this
change does not alter any code or data, just comments.
* Theory, zone.tab: Deemphasize the role of countries in choosing
location names, as they tend to introduce political conflict
during maintenance, and country information isn't needed for
typical uses of the database.
* Theory: Say that names should differ in more than just case, and why;
and explain why 'backward' means old names will continue to work.
(thanks to Norbert Lindenberg for spotting these issues).
Update citation date and URL.
* iso3166.tab: Mention latest maintenance update.
Update citation URL.  Add missing comma for BQ.
Be more consistent about abbreviating Sint like Saint.
Mention SX "Dutch part" for consistency with MF "French part".
* iso3166.tab, zone.tab: Add legal/territorial disclaimer.
* zone.tab: Say that country/zone overlaps can occur in both
directions, and that column 2 need not lie within column 1.
(Asia/Jerusalem): Change the coordinates from a sloppy value,
taken from an old astrology book, to a more-precise value, the
site of city hall.  The sloppy value sparked some controversy and
the hope is that the more-precise value will be a bit less
controversial.