tests/test-gendoc-da.t

py3: replace file() with open() in test-import.t

file() is not present in Python 3.
This patch also adds a b'' prefix to make sure we write bytes in Python 3.

Differential Revision: https://phab.mercurial-scm.org/D2123

#require docutils gettext

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