Version Control With Subversion Source

Thanks to Vlad Georgescu <vgeorgescu@...> for his excellent
notes in notes/sasl.txt. This is essentially a rewrite of the same
content.

* src/en/book/ch06-server-configuration.xml
(Using <command>svnserve</command> with SASL): fill out section.

* src/en/book/ch00-preface.xml: add Vlad to acknowledgements.