tests/test-gendoc-pt_BR.t

color: move 'write-err' logic to the core ui class

This is similar to what we needed for 'write', we move the logic from the
extension to the core class. Beside the dispatch to 'win32print', we just apply
label to the argument.

#require docutils gettext

  $ $TESTDIR/check-gendoc pt_BR
  checking for parse errors