Need to repeat ourselves, apparently.

Although it appeared to test fine on-device, Litmus doesn't appear to handle the case where you are applying multiple responsive rules.  Having "drop" automatically include "fill" class on tds caused inconsistent layout problems in Litmus compatibility results - some columns would drop, others would not.  I think it is a bug in Litmus but just as a precaution, I'll re-introduce a little bit of repetition to make sure it doesn't happen on device.