packaging: prepare version 6.0.0

merged with future 6.0 No output changed.

test-compat-hg-3.9: merge with future 6.0

merge with future 6.0.0

merge with default We are getting close to cutting a 6.0.0

readme: mention the fix for issue4354

checkheads: add a small debug message in case were we give up fast When node is unknown we assume it will stay. Yet, we might have markers to it that are going to be pushed. However, we do not have branch (ancestors) information unless we are very lucky an all of them are pruned. So for now we do not do anything assuming this will be rare. We still add a small debug message to help detecting such situation in the future.

checkheahds: switch algorithm to use pushed markers instead We now checks if markers involved in the push are relevant to nodes in the branch we try to replace. The approach is simpler and more robust. A test showing the limitation of the previous approach is added.

checkheads: add test where the rewrite of the other branch is not direct This will help testing that our logic is properly transitive.

check-heads: add tests about old heads indirectly pruned