Backport of htdbm documentation addition, as submitted by

Matt Brubeck <mbrubeck@cs.hmc.edu>.  Add manpage, update
transformations, add props.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@161235 13f79535-47bb-0310-9956-ffa450edef68