The markers pruning a node was not directly considered relevant for the pruned
node, only to its parents.
This went unnoticed during obsmarkers exchange because all
ancestors of the pruned node would be included in the computation.
This still affects obsmarkers exchange a bit since "inline" prune markers would
be ignored (see second test case). This went unnoticed, because in such case,
we always push another obsolescence markers for that node.
We add explicit tests covering this case.
(The set of relevant changeset is use in the obsmarkers discovery protocol used
in the evolve experimental extension, the impact will be handled on the
extension side).
The logic around obsmarkers "relevant" to a set of revs have a couple of test
around in other places but no systematic testing. In addition, all the current
testing focus on the exchange case (we looks at relevant markers for
'::heads').
For bundles, we'll need something a bit different. We'll no longer have set of
revision going down to the repository roots. So we'll have to test these cases
too. In addition, stripping obsmarkers will introduce new logic around
obsmarkers that will need testing too. So a new test file make sense here.
We start with a simple tests, more advanced cases are coming in the next
changesets. The extra testing catch a minor bug (later in the series).
