On the 1.7.x-issue4460 branch: Partially merge r1311747 from trunk

Didn't merge the test just the changes to make_diff_header()


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x-issue4460@1563070 13f79535-47bb-0310-9956-ffa450edef68