Backport:

Backport:

  *) mod_dav: Add method_precondition hook. WebDAV extensions define
     conditions that must exist before a WebDAV method can be executed.
     This hook allows a WebDAV extension to verify these preconditions.
     trunk patch: http://svn.apache.org/r1879339
                  http://svn.apache.org/r1879340
     2.4.x patch: https://svn.apache.org/repos/asf/httpd/httpd/patches/2.4.x/httpd-2.4-dav-preconditions1.patch
     +1: minfrin, jim, ylavic (by inspection)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1892514 13f79535-47bb-0310-9956-ffa450edef68