This article was originally published online on 10 December 2015 with a footnote designated to the incorrect author. The footnote “Current address: Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada” should have been assigned to the author Vern Paulsen. AIP Publishing apologizes for this error. All online versions of the article were corrected on 11 December 2015; the article is correct as it appears in the printed version of the journal.