discovery: prevent crash caused by prune marker having no parent data If a marker has no parent information, parents field is set to None, which caused TypeError. I think this shouldn't normally happen, but somehow I have such marker in my repo.

color: point to the global help in the example hgrc This is probably the best way to have users learn more is they need too.

color: reflect the new default in the example hgrc Color is enabled by default so un-commenting the line would not have any effect. We'll point to the help in the next changeset.