Have mod_dav deal with errors that happen during a streamy provider

response.

* mod_dav.c (dav_method_propfind, dav_method_report): if the dav
    provider throws an error in the middle of streaming a response,
    have mod_dav log an error and abort the connection.

Submitted by: Ben Collins-Sussman <sussman@collab.net>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@100309 13f79535-47bb-0310-9956-ffa450edef68