Version Control With Subversion Source

* src/en/book/ch09-reference.xml
(svn.ref.svnserve.sw): Point folks to new high-level logging
section.
(svn.ref.mod_dav_svn.conf.logging): Move high-level logging details
from here...

* src/en/book/ch06-server-configuration.xml
(svn.serverconfig.operational-logging): ... to here.
(svn.serverconfig.httpd.extra.logging): Update xref per the
aforementioned relocation of logging details.