Sorry, please hold on about the review. I didn't run Jenkins before asking for review, and Jenkins failed. I'll investigate.

Fixed the previous problem. Jenkins passed: https://ci.lsst.codes/job/stack-os-matrix/label=centos-7/5943//console

Looks good; thanks. My only comment is really tangential to the work you've done here: rather than simply labelling something a "placeholder implementation" in the code, if we know it needs to be replaced we should have a ticket for it. You didn't add the comment, but since you're touching that piece of code maybe you could take the opportunity to make sure such a ticket exists and is referred to in the comments.

Other than that, good to merge.

Thank you for your review! I don't think there is a ticket for expanding the fringe correction yet; I'll search and create one if none is found, and make notes in the code.

Created DM-4441 for multiple frame fringe subtraction, and added the ticket number to the comment in the code.

Merged to master.