Version Control With Subversion Source

* src/en/book/ch00-preface.xml
(svn.preface.howread): Add paragraph about top-down vs. bottom-up
learning. I'm tired of talking about this subject with in every
conversation I have with people about our book. I think it's useful
meta-philosophy.. :-)

* src/en/book/appa-quickstart.xml
(svn.intro): Remove terminology from here, now that it's mentioned
in the Preface. Simplify the appendix introduction, wrap the 2nd
paragraph in a <warning>, so impatient people actually see it.