addchangegroup: use a postrelease callback to call changegroup hook

This is will allow addchangegroup to drop lock related code.

mercurial/localrepo.py

@@ -2003,11 +2003,8 b' class localrepository(repo.repository):'
             cl.finalize(trp)
 
             tr.close()
-        finally:
-            tr.release()
-            if lock:
-                lock.release()
 
+            def postaddchangegroup():
         if changesets > 0:
             # forcefully update the on-disk branch cache
             self.ui.debug("updating the branch cache\n")
@@ -2016,8 +2013,14 b' class localrepository(repo.repository):'
                       source=srctype, url=url)
 
             for n in added:
-                self.hook("incoming", node=hex(n), source=srctype, url=url)
+                        self.hook("incoming", node=hex(n), source=srctype,
+                                  url=url)
+            self._postrelease(postaddchangegroup)
 
+        finally:
+            tr.release()
+            if lock:
+                lock.release()
         # never return 0 here:
         if dh < 0:
             return dh - 1