obsolete: fix relevant-obsmarkers computation on pruned changeset 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).

test: add a test file for relevant obsmarkers and its usage 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).