When svn.pushmergeinfo is set, the target branch is included in the
mergeinfo if it was previously merged into one of the source branches.
SVN does not do this.

Remove merge target branch path from resulting mergeinfo when
svn.pushmergeinfo is set to better match the behavior of SVN. Update the
svn-mergeinfo-push test.

[ew: 80 columns]
Signed-off-by: NMichael Contreras <michael@inetric.com>
Reported-by: NAvishay Lavie <avishay.lavie@gmail.com>
Acked-by: NEric Wong <normalperson@yhbt.net>