Quoting Marc Lustig:
Although we have installed SVN 1.6.6, the web-page delivered reports 1.4.6Could someone advise how to identify the version of mod_dav_svn apache-module that is installed?
I think you've already discovered how: look on the web page. It says 1.4.6. You have mod_dav_svn from Subversion 1.4.6. Or at least, you did when Apache started. If you've since then updated mod_dav_svn, restart Apache to see this change.