Version Control With Subversion Source

Book work.

* appa.xml: Massive re-org and changes to the appendix. Ready for review.

* ch04.xml: explain that 'svn switch' takes a -r option, and that it
preserves local mods as well. Thanks to M. S. Sriram
<mssriram@...> for pointing out that this idea was missing
in the book.

* ch02.xml: add some headings and rewordings, as suggested by Mason
Thomas <mlt_svn@...>.