Now that we have apr_datum_t, convert some uses of dav_datum over to

apr_datum_t (the two are equivalent).

Expose some of the DAVFS' internal DBM cover functions and have the locking
code use them directly, rather than thru the vtable. That vtable will be
changing shortly, so this shift is needed.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91064 13f79535-47bb-0310-9956-ffa450edef68