Comment #34 on issue 2801 by [email protected]: Patch: Approximates cross-staff slurs in VerticalAxisGroup vertical-skylines.
http://code.google.com/p/lilypond/issues/detail?id=2801
Given the artifacts in the latest tests of issue 2815, I lean strongly towards reverting this patch for now. <URL:http://code.google.com/p/lilypond/issues/detail?id=2815#c13>
