push: refuse to push bumped changeset This applies the same logic as used for `obsolete` and `unstable` changesets. Refuse to push them without force. We'll probably want to factor this logic with two new functions `pctx.troubled()` and `ctx.troubles()`. But I'm waiting for the third "trouble" to make it into core.

obsolete: simplify push abort message to: push includes xxx changeset: yyyyyyyyyy

context: add a `bumped` method to `changectx` Same as `unstable()`, returns true if the changeset is bumped.

obsolete: add a flag that allows fixing "bumped" changeset The first obsolescence flag is introduced to allows for fixing the "bumped" changeset situation. bumpedfix == 1. Creator of new changesets intended to fix "bumped" situation should not forget to add this flag to the marker. Otherwise the newly created changeset will be bumped too. See inlined documentation for details.

debugobsolete: add --flags option This options allows to specify the `flag` part of obsolete markers. For details about marker flags, check the `mercurial/obsolete.py` documentation. Some random flag are added to a marker to test this feature.

revset: add a bumped revset Select bumped changesets.

obsolete: add the detection of bumped changeset. Bumped changesets are non-public changesets that tries to succeed a public() changeset.

obsolete: have `allsuccessors` takes a list of nodes Additional logic, used to detect mutable history troubles, will need to quickly compute successors of a whole set of changeset.

obsolete: rename `anysuccessors` into `allsuccessors` The "any" prefix looks like it returned a boolean. `allsuccessors` is more accurate.

obsolete: rename `getobscache` into `getrevs` The old name was not very good for two reasons: - caller does not care about "cache", - set of revision returned may not be obsolete at all. The new name was suggested by Kevin Bullock.