changegroup: use tr.hookargs when calling pretxnchangegroup hooks

So that other parties using the transaction can put information in our hook
calls.

mercurial/changegroup.py

@@ -675,9 +675,8 b' def addchangegroup(repo, source, srctype'
             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)
+            repo.hook('pretxnchangegroup', throw=True, source=srctype,
+                      url=url, pending=p, **tr.hookargs)
 
         added = [cl.node(r) for r in xrange(clstart, clend)]
         publishing = repo.ui.configbool('phases', 'publish', True)