push: put obsmarkers in the same bundle2 than changeset When client is Mercurial 3.1 and server have proper evolve version and both side have bundle2 enabled, we'll includes a part containing obsolescence markers. When obsmarkers are included to the main bundle2 push, they will failed to be pushed if the changeset failed to be pushed (and reciprocally).

push: extract obsmarkers discovery in a dedicated function The need to factorise the computation of the markers to send in a dedicated function. This prepare the inclusion of obsmarkers in an atomic bundle2 push. For now, when obsmarkers are pushed using bundle2, they are still doing it on their own, in a dedicated bundle2 push.