test-ssh: verify that stderr from remote is printed (issue4336)

The issue fixed in the previous patch was uncovered by implementing an
extension that printed additional output locally before the push command
completed. This test emulates that.

If this change is applied before the previous patch, the test will fail
on Linux, with the local output being printed before the "remote: "
lines.

tests/test-ssh.t

@@ -360,6 +360,47 b' Test hg-ssh in read-only mode:'
 
   $ cd ..
 
+stderr from remote commands should be printed before stdout from local code (issue4336)
+
+  $ hg clone remote stderr-ordering
+  updating to branch default
+  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ cd stderr-ordering
+  $ cat >> localwrite.py << EOF
+  > from mercurial import exchange, extensions
+  > 
+  > def wrappedpush(orig, repo, *args, **kwargs):
+  >     res = orig(repo, *args, **kwargs)
+  >     repo.ui.write('local stdout\n')
+  >     return res
+  > 
+  > def extsetup(ui):
+  >     extensions.wrapfunction(exchange, 'push', wrappedpush)
+  > EOF
+
+  $ cat >> .hg/hgrc << EOF
+  > [paths]
+  > default-push = ssh://user@dummy/remote
+  > [ui]
+  > ssh = python "$TESTDIR/dummyssh"
+  > [extensions]
+  > localwrite = localwrite.py
+  > EOF
+
+  $ echo localwrite > foo
+  $ hg commit -m 'testing localwrite'
+  $ hg push
+  pushing to ssh://user@dummy/remote
+  searching for changes
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 1 changesets with 1 changes to 1 files
+  remote: KABOOM
+  local stdout
+
+  $ cd ..
+
   $ cat dummylog
   Got arguments 1:user@dummy 2:hg -R nonexistent serve --stdio
   Got arguments 1:user@dummy 2:hg -R /$TESTTMP/nonexistent serve --stdio
@@ -387,3 +428,5 b' Test hg-ssh in read-only mode:'
   Got arguments 1:user@dummy 2:hg -R 'a repo' serve --stdio
   Got arguments 1:user@dummy 2:hg -R 'a repo' serve --stdio
   Got arguments 1:user@dummy 2:hg -R 'a repo' serve --stdio
+  Got arguments 1:user@dummy 2:hg -R remote serve --stdio
+  changegroup-in-remote hook: HG_NODE=65c38f4125f9602c8db4af56530cc221d93b8ef8 HG_SOURCE=serve HG_URL=remote:ssh:127.0.0.1