tests/test-gendoc-el.t

ui: optimize buffered write with no label

This was spotted while making fastannotate faster again after ditching its
own formatter. Since I'm going to inline _write() into ui.write(), I decided
to include this patch in this series.

Here, the cost of '(self.label(a, label) for a in args)' was significant
in hot loops.

#require docutils gettext

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