Comment #60 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
The patch doesn't do slurs over line breaks yet, but otherwise handles Keith's test case (op45.ly) much better and errs on the side of caution when approximating slurs. At worst this results in the old collisions, but often it introduces at least a bit of space.
