Merge branch 'jk/bisect-final-output'

Merge branch 'jk/bisect-final-output'

The final report from "git bisect" used to show the suspected
culprit using a raw "diff-tree", with which there is no output for
a merge commit.  This has been updated to use a more modern and
human readable output that still is concise enough.

* jk/bisect-final-output:
  bisect: make diff-tree output prettier
  bisect: fix internal diff-tree config loading
  bisect: use string arguments to feed internal diff-tree