ambiata/ivory — pull request #413 by charleso (2014-11-04 02:39:37+00:00)
Title: Ignore tombstone values completely in days_since_latest

Given that tombstones are impossible for sets I guess this doesn't necessarily "fix" anything. But it brings the "days_since" functions inline with each other. The "days_since_*_by" functions were already doing this inadvertently.