For our scintillating “Back to School” post, we’ll discuss 11 U.S.C. § 1129(d), which deals with those rare Chapter 11 plans whose “principal purpose” is the “avoidance of taxes.” For most, including judges, § 1129(d) is an afterthought. Until recently, it only crept into my practice by accident: I’ve got a 10 a.m. confirmation…