1.8.x backport issue #4476 - svnsync with r0 mergeinfo - resolve the veto

[Julian Foad]

Hi Philip. I've updated the 1.8.x nomination of issue #4476 - svnsync with r0 
mergeinfo - to resolve the concern that's the subject of your veto. Please 
could you review and remove your veto if possible. Thanks.

- Julian