diff: extract function for getting possibly re-merged parent to diff against...
diff: extract function for getting possibly re-merged parent to diff against
We'll want to reuse the logic that `hg diff --change` with
`diff.merge` uses. At least `hg log -p` should reuse it. This patch
therefore extracts that code to a function.
Differential Revision:
https://phab.mercurial-scm.org/D9957
