branchmap: improve invalid cache message when reading This factors out the generation of the message. This helps future error reporting when reading cache for filtered repository.

histedit: allow operation from non-head if obsolete is enabled Obsolescence markers can represent this situation just fine. Rewritten revisions are marked as precursors of the ones creates by histedit. Unaffected descendants become "unstable". If obsolescence is not enabled we keep the current behavior of aborting. This new behavior only applies when obsolete is enabled and is subject to future discussion and changes.

rebase: allow non-head rebase-set when obsolete is enabled Obsolescence markers can represent this situation just fine. Rebased revisions are marked as precursors of the ones create by rebase. Unrebased descendants becomes "unstable". If obsolescence is not enabled we keep the current behavior of aborting. This new behavior only applies when obsolete is enabled and is subject to future discussion and changes.

amend: allow amend of non-head when obsolete is enabled Obsolescence marker can represent this situation just fine. The old version is marked as precursor of the new changeset. All its descendants become "unstable". If obsolescence is not enabled we keep the current behavior of aborting. This new behavior only applies when obsolete is enabled and is subject to future discussion and changes.

obsolete: factorise troubles detection during push The use of the two methods introduced earlier allows a factorisation of the push code preventing push of troubled changeset.

obsolete: introduce a troubles method on context A troubled changeset may be affected by multiple trouble at the same time. This new method returns a list of all troubles affecting a changes.

obsolete: introduce a troubled method on context Allows to quickly check if a changeset is affected by any troubles. (troubles are: unstable, bumped and divergent)

tests: fix windows test failures