Backported.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1486455 13f79535-47bb-0310-9956-ffa450edef68
mod_dav: Sending a If or If-Match header with an invalid ETag doesn't
result in a 412 Precondition Failed. PR54610

trunk patch: http://svn.apache.org/r1476604
Submitted by: Timothy Wood <tjw omnigroup.com>
Reviewed by: minfrin, jim, jorton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1486456 13f79535-47bb-0310-9956-ffa450edef68