* Rolled all of the groupdav*.[ch] files way back to version 3851. Something

* Rolled all of the groupdav*.[ch] files way back to version 3851.  Something
  somewhere in willi's doxygen changes broke GroupDAV protocol.  Since I was
  unable to figure out where, I had to roll it all back.
* The good news is that the server-absolute URL's do work after all, so I
  reinstated that.