py3: fix type of default username

contrib/python3-whitelist

@@ -48,6 +48,7 b' test-command-template.t'
 test-commit-amend.t
 test-commit-unresolved.t
 test-commit.t
+test-committer.t
 test-completion.t
 test-config-env.py
 test-config.t

mercurial/ui.py

@@ -800,7 +800,8 b' class ui(object):'
             user = self.prompt(_("enter a commit username:"), default=None)
         if user is None and not self.interactive():
             try:
-                user = '%s@%s' % (util.getuser(), socket.getfqdn())
+                user = '%s@%s' % (util.getuser(),
+                                  encoding.strtolocal(socket.getfqdn()))
                 self.warn(_("no username found, using '%s' instead\n") % user)
             except KeyError:
                 pass