also str representation of unicode character is different.

page templates unicode resolver already takes care of coercing when
needed and this is directly compatible with python2 and python3
Co-authored-by: Kazuhiko SHIOZAKI <kazuhiko@nexedi.com>

This only works on python2

for same reason as the xhtml_style version, there is no problem with
having more than one listbox, see d2dedca3 (core: remove useless log
in Base_callDialogMethod, 2020-07-03)

This prevents one failing test to make all subsequent tests to fail

this is removed from python3, it was not so useful here either

use sys.maxsize, see discussion on
nexedi/erp5!1751 (comment 203735)

assertCountEqual is the new python3 name.

Implement this in backportUnittest.py and also move the existing similar
patches (assertRaisesRegex and assertRegex).