branchmap: issue a single call to `ancestors` for all heads There is no reason to make multiple calls. This provides a massive speedup for repo with a lot of heads. On a strongly headed repo this gives humble speedup in simple case: from 8.1097 to 5.1051 And massive speedup in other case: from 7.8787 to 0.1984

test-ancestor: add a test for `ancestor` with ancestry within the initset I was wondering if revisions in the initial set that are still ancestors of other elements in the initial set were yielded by `changelog.ancestors`. I now have my answer (they do) and Mercurial has a new test.

bundle2: pull obsmarkers relevant to the pulled set through bundle2 We use the new `obsheads` argument to retrieve them in a bundle2 part at the same time as the changegroup.