mod_dbd: Key the storage of prepared statements on the hex string

value of server_rec, rather than the server name, as the server name
may change (eg when the server name is set) at any time, causing
weird behaviour in modules dependent on mod_dbd.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@466641 13f79535-47bb-0310-9956-ffa450edef68