discovery: properly filter changeset in 'peer.known' (issue4982) The 'peer.known' call (handled at the repository level) was applying its own manual filtering (looking at phases) instead of relying on the repoview mechanism. This led to the discovery finding more "common" node that 'getbundle' was willing to recognised. From there, bad things happen, issue4982 is a symptom of it. While situations like described in issue4982 can still happen because of race conditions, fixing 'peer.known' is important for consistency in all cases. We update the code to use 'repoview' filtering. This lead to small changes in the tests for exchanging obsolescence marker because the discovery yields different results. The test affected in 'test-obsolete-changeset-exchange.t' is a test for issue4982 getting back to its expected state.