transaction: issue "new obsmarkers" message at the end of the transaction Instead of making bundle2 code responsible for this, it seems better to have it handled and the transaction level. First, it means the message will be more consistently printed. Second it means we won't spam the message over and over if the data arrive in multiple piece. Third, we are planning to move other similar message at the same level (for the same reason) so having them all at the same location will help us to control the order they are displayed.

debugobsolete: also issue the "new obsmarkers" messsage We are going to improve the way this message is issued in the core codebase. This will make it appears for `hg debugobsolete` too. Since this seems like a good idea, we make the output change in a previous changesets to clarify the next changeset.