transaction: track new obsmarkers in the 'changes' mapping

The obsstore collaborate with transaction to make sure we track all the
obsmarkers added during a transaction. This will be useful for various usages:
hooks, caches, better output, etc.

This is the seconds kind of data added to tr.changes (first one was added revisions)

mercurial/localrepo.py

@@ -1083,6 +1083,7 b' class localrepository(object):'
                                      validator=validate,
                                      releasefn=releasefn)
         tr.changes['revs'] = set()
+        tr.changes['obsmarkers'] = set()
 
         tr.hookargs['txnid'] = txnid
         # note: writing the fncache only during finalize mean that the file is

mercurial/obsolete.py

@@ -613,6 +613,9 b' class obsstore(object):'
                 # XXX: f.close() == filecache invalidation == obsstore rebuilt.
                 # call 'filecacheentry.refresh()'  here
                 f.close()
+            addedmarkers = transaction.changes.get('obsmarkers')
+            if addedmarkers is not None:
+                addedmarkers.update(new)
             self._addmarkers(new)
             # new marker *may* have changed several set. invalidate the cache.
             self.caches.clear()