Handle chdir() error, with test.

core/builtin.py

@@ -431,7 +431,12 @@ def Cd(argv, mem):

  # Save OLDPWD.
  state.SetGlobalString(mem, 'OLDPWD', os.getcwd())
  os.chdir(dest_dir)
  try:
    os.chdir(dest_dir)
  except OSError as e:
    # TODO: Add line number, etc.
    util.error("cd %r: %s", dest_dir, os.strerror(e.errno))
    return 1
  state.SetGlobalString(mem, 'PWD', dest_dir)
  return 0

spec/builtins.test.sh

@@ -55,6 +55,12 @@ cd
test $(pwd) = "$HOME" && echo OK
# stdout: OK

### cd to nonexistent dir
cd /nonexistent/dir
echo status=$?
# stdout: status=1
# OK dash/mksh stdout: status=2

### pushd/popd
set -o errexit
cd /