Have mod_dav_svn return "500 SERVER ERROR" rather than "409 CONFLICT"
when a commit fails and the reason is not SVN_ERR_FS_CONFLICT.

* subversion/mod_dav_svn/version.c
  (dav_svn__checkin, merge): Return 500 when commit error is not a conflict.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1490684 13f79535-47bb-0310-9956-ffa450edef68