Missing subtags 003 and 172

[Doug Ewell]

Here's another attempt at the diagram showing how 003 "fits" into the UN
M.49 hierarchy.  Some combination of mailing software and
digest-building software minced up my original diagram.  A monospaced
font is advised.

001 World
  019 Americas
    021 Northern America   <-----------------+
      419 Latin America and the Caribbean    |
        005 South America                    +- 003 North America
        013 Central America   <--------------+
        029 Caribbean   <--------------------+

--Doug