Added gunk from old "auth_dbm.html" describing some implementation

issues.  This so we can nuke auth_dbm.html, which really doesn't have
a home... also fixed some minor typos.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@76999 13f79535-47bb-0310-9956-ffa450edef68