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.

color: point to the config help in global help topic We point out at the help of the config option for user who wants to learn more about the possible config value. The suggested command returns some other extra (color related) results, but this is bug to fix outside of the freeze.

color: reflect the new default in global help topic We point out that color is enabled by default.

docs: describe ui.color consistently with --color The --color option is described to accept "boolean, always, auto, never, or debug". Let's use a similar description for ui.color. Also fix the formatting to use double quotes as we seem to use for about half the values in config.txt (the other half uses double backticks). Also use uppercase Boolean for consistency within the file.