For folks who wouldn't click on the links, the title of the issue is "doctest _load_testfile function -- newline handling seems incorrect", it was filed in 2008 and has many comments, plus diffs dating back to 2008.
The Pull Request title is "Fix newline conversion when doctest.testfile loads from a package whose loader has a get_data method", it looks relatively straightforward and thorough. Presumably it's based on the diffs from the issue.
The author of the issue and PR are the same as the OP above.
This will be a doozie for whoever wants to volunteer!