bundle2-wireproto: properly propagate the server output on error (issue4594)

In case of errors, output parts salvaged from the reply bundle are re-injected
into the bundle carrying the exception.

We still need to fix the situation for non-wireprotocol push.

mercurial/wireproto.py

@@ -858,6 +858,8 b' def unbundle(repo, proto, heads):'
                 return pusherr(str(exc))
 
         bundler = bundle2.bundle20(repo.ui)
+        for out in getattr(exc, '_bundle2salvagedoutput', ()):
+            bundler.addpart(out)
         try:
             raise
         except error.BundleValueError, exc:

tests/test-bundle2-exchange.t

@@ -567,6 +567,10 b' Doing the actual push: hook abort'
   $ hg -R main push ssh://user@dummy/other -r e7ec4e813ba6
   pushing to ssh://user@dummy/other
   searching for changes
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 1 changesets with 1 changes to 1 files
   abort: pretxnclose.failpush hook exited with status 1
   remote: pre-close-tip:e7ec4e813ba6 draft 
   remote: transaction abort!
@@ -576,6 +580,10 b' Doing the actual push: hook abort'
   $ hg -R main push http://localhost:$HGPORT2/ -r e7ec4e813ba6
   pushing to http://localhost:$HGPORT2/
   searching for changes
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 1 changesets with 1 changes to 1 files
   abort: pretxnclose.failpush hook exited with status 1
   [255]