filemerge: default change/delete conflicts to 'leave unresolved' (BC)
It makes far more sense to leave these conflicts unresolved and kick back to
the user than to just assume that the local version be chosen. There are almost
certainly buggy scripts and applications using Mercurial in the wild that do
merges or rebases non-interactively, and then assume that if the operation
succeeded there's nothing the user needs to pay attention to.
(This wasn't possible earlier because there was no way to re-resolve
change/delete conflicts -- but now it is.)