Make earliestKnownWorkingRev construct a 'least common descendant' revset, so we don't have to think about merges when adding to the list.  The known cases are (1) between -n and -D and (2) between ion and ggc.
Make earliestKnownWorkingRev construct a 'least common descendant' revset, so we don't have to think about merges when adding to the list.  The known cases are (1) between -n and -D and (2) between ion and ggc.

MozillaSecurity/funfuzz,MozillaSecurity/funfuzz,nth10sd/funfuzz,nth10sd/funfuzz,nth10sd/funfuzz,MozillaSecurity/funfuzz