sshserver: flush stream after command dispatch

I am not sure why this is not working as expected, but without this client might
not see some important output. Without this patch moving some output at
transaction closing time makes it disapear for ssh client in various sitaution.

mercurial/wireprotoserver.py

@@ -657,6 +657,8 b' def _runsshserver(ui, repo, fin, fout, e'
                 continue
 
             rsp = wireprotov1server.dispatch(repo, proto, request)
+            repo.ui.fout.flush()
+            repo.ui.ferr.flush()
 
             if isinstance(rsp, bytes):
                 _sshv1respondbytes(fout, rsp)

tests/test-bookmarks-corner-case.t

@@ -200,8 +200,8 b' Check raced push output.'
   $ cat push-output.txt
   pushing to ssh://user@dummy/bookrace-server
   searching for changes
+  remote: setting raced push up
   remote has heads on branch 'default' that are not known locally: f26c3b5167d1
-  remote: setting raced push up
   remote: adding changesets
   remote: adding manifests
   remote: adding file changes

tests/test-ssh-proto.t

@@ -104,6 +104,7 b' I/O logging works'
   $ hg debugserve --sshstdio --logiofd 1 << EOF
   > hello
   > EOF
+  e> flush() -> None
   o> write(4) -> 4:
   o>     440\n
   o> write(440) -> 440:
@@ -119,6 +120,7 b' I/O logging works'
   capabilities: batch branchmap $USUAL_BUNDLE2_CAPS$ changegroupsubset getbundle known lookup protocaps pushkey streamreqs=generaldelta,revlogv1,sparserevlog unbundle=HG10GZ,HG10BZ,HG10UN unbundlehash
 
   $ cat $TESTTMP/io
+  e> flush() -> None
   o> write(4) -> 4:
   o>     440\n
   o> write(440) -> 440: