test-compat: merge stable into mercurial-5.2

topic: hg <= 4.8 compatibility for wrapping exchange._checkpublish() phase-divergent update to 1a81bbc94d45:

branching: merge with stable

topic: check that exchange._checkpublish() exists before wrapping it

head-checking: also test single head enforcement with topic They are an important part of why we want this.

head-checking: ignore obsoleted section when checking head creation locally Same as for the server side check, these do not need to be taken in account.

head-checking: ignore obsolete section when checking for single heads This overwrite the core code that enforce single heads to ignore obsolete section. That way older obsolete version of a branch no longer prevent the new version to be pushed.

head-checking: update changelog

head-checking: add test variant mixing branch and topics

head-checking: add test variants with topics

head-checking: backport fix from 7d5455b988ec See 7d5455b988ec for details. Having a version in the evolve repository allow us to check the behavior when topic is enabled. It will also become the base of further head checking fix and topic compatibility.

head-checking: filter out obsolete heads when checking for new heads This does not affect any tests right now, but this will be useful for the next changeset. This is also the start of a more aggressive removal of obsolete heads in places where it does not make sense to take them into account.