chapter 3 fixes

[Jon Lapham]

Changes to Chapter 3:

-Some small text changes
-Added the salary tax stuff... it is needed for chapter 4
-Rebuilt the basic_tree.png mage to include the salary tax stuff

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  Jon Lapham  <lapham at extracta.com.br>          Rio de Janeiro, Brasil
  Work: Extracta Moléculas Naturais SA     http://www.extracta.com.br/
  Web: http://www.jandr.org/
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