This is patched to DateTime.DateTime._dt_reconstructor but we don't
want _dt_reconstructor to appear in pickles, especially business
templates ones.

This backports parts of zope commit bb7837c66 (Explicitly make all
classes new-style., 2017-09-15) and 173658008 (Fix unpickling of instances
those base class changed to a new-style class. (#208), 2017-10-24).

This is done for two reasons:
 - so that business template XML are same when exported from zope4
   and from zope2
 - so that a business template created from zope4 can still be
   installed on zope2.

This is used to trigger recompilation of bytecode, but we don't
export the byte code so we don't need to export it.
This also prevent diffs when the Script_magic changed, like it's the
case with Products.PythonScripts 4.2 , with commit 590125a (Force
recompilation of scripts., 2017-10-23).

These properties are supposed to never be set on ERP5 documents.

See https://lab.nexedi.com/nexedi/erp5/blob/34f4ae37/product/ERP5Type/Constraint/PropertyTypeValidity.py#L65

This properties are not used, no need to have them exported

If there's an error during the --save setup, we don't need to run
the --load steps, because test failed already and if they don't
fail in --load step, it would be a case where some errors are not
reported.

Usually we run tests with two nodes, so when there's a conflict it's
always between the "main" node and the processing node, so we always
have a distributing node during conflict.

But when running with, for example, 2 nodes (the main node + 2 nodes),
the conflict might occur between the two processing nodes and after
the resolution we still don't have a distributing node.

When looking up a document by reference, using getDocumentValueList from
the context of a web site / web section might not find the documents,
depending on the predicates defined on the web site / web section.

This gadget looks up a document by reference, by using
getDocumentValueList on the context of the web section.
getDocumentValueList also applies the criterions from the context, but
because web page references are already unique, adding more criterions
can just cause the document to be not found and the gadget to display
the "No document" error.

This sort was based on the id of the role definition but this did not
work when the type definition had more than 10 documents, because:

    >>> sorted(['1', '2', '10'])
    ['1', '10', '2']

This switches to an approach of converting the id to integer, with a
fallback in case the id generator is customized.

cause by nexedi/erp5!1726

use calendar module and public DateTime API instead.

This ensures that we don't break more.

We have code depending on these attributes, they were used in pattern
like this:

```py
try:
  DateTime(user_input)
except DateTime.DateError:
  error("invalid date")
```

so it's safer to keep the attributes for now, since we are already
patching a lot

We have too much code depending on this behavior, so we keep this patch
for now.

By using iso format we create dates in UTC timezone

This is a context manager which temporary allow to change the time zone.

It is not thread safe and intended to be used in tests only, to replace
setTimeZoneToUTC and setTimezone methods by something unified which
makes the transition to DateTime 4 easier, because changing timezone
was done by patching private attributes and the DateTime 4 use different
attributes.

Use calendar module instead. These API depends on current locale, but
we don't set the locale in ERP5, so these remain in English

This is just hiding problem and does not seem needed.