changegroup: use the 'postclose' API on transaction

The post-transaction hooks run after the lock release (because hooks may want to
touch the repository), but they must only run if the transaction is successfully
closed.

We use the new 'addpostclose' method on transaction to register a callback
installing this post-lock-release call.

mercurial/changegroup.py

@@ -788,9 +788,6 b' def addchangegroup(repo, source, srctype'
             # strip should not touch boundary at all
             phases.retractboundary(repo, tr, targetphase, added)
 
-
-        tr.close()
-
         if changesets > 0:
             if srctype != 'strip':
                 # During strip, branchcache is invalid but coming call to
@@ -819,7 +816,11 b' def addchangegroup(repo, source, srctype'
                             "%s incoming changes - new heads: %s\n",
                             len(added),
                             ', '.join([hex(c[:6]) for c in newheads]))
-            repo._afterlock(runhooks)
+
+            tr.addpostclose('changegroup-runhooks-%020i' % clstart,
+                            lambda: repo._afterlock(runhooks))
+
+        tr.close()
 
     finally:
         tr.release()

tests/test-bundle2-exchange.t

@@ -462,7 +462,6 b' Doing the actual push: hook abort'
   searching for changes
   transaction abort!
   rollback completed
-  changegroup hook: HG_BUNDLE2-EXP=1 HG_NODE=e7ec4e813ba6b07be2a0516ce1a74bb4e503f91a HG_SOURCE=push HG_URL=push
   abort: b2x-pretransactionclose.failpush hook exited with status 1
   [255]
 
@@ -472,7 +471,6 b' Doing the actual push: hook abort'
   abort: b2x-pretransactionclose.failpush hook exited with status 1
   remote: transaction abort!
   remote: rollback completed
-  remote: changegroup hook: HG_BUNDLE2-EXP=1 HG_NODE=e7ec4e813ba6b07be2a0516ce1a74bb4e503f91a HG_SOURCE=serve HG_URL=remote:ssh:127.0.0.1
   [255]
 
   $ hg -R main push http://localhost:$HGPORT2/ -r e7ec4e813ba6