PSA: Check the entire commit messages when merging PRs

I was trying to clean up the commit message in the text box that pops up
when you click the green "Confirm squash and merge" button, but it looks
like I have been unsuccessful. It looks like a couple of Mark's recent
commits had similar issues.

I believe the problem is that the text box defaults to only a couple lines
but copies of the message for each commit appear in subsequent lines. So,
remember to delete any extra lines when merging.