addchangegroup: register data in tr.hookargs

We are registering data related to the process into the transaction hook data.
This lets other parties using the same transaction get informed of the
addchangegroup result.

mercurial/changegroup.py

@@ -673,6 +673,8 b' def addchangegroup(repo, source, srctype'
 
         if changesets > 0:
             p = lambda: cl.writepending() and repo.root or ""
+            if 'node' not in tr.hookargs:
+                tr.hookargs['node'] = hex(cl.node(clstart))
             repo.hook('pretxnchangegroup', throw=True,
                       node=hex(cl.node(clstart)), source=srctype,
                       url=url, pending=p)