When migrating a database, load_marked_modules will be called multiple times, alternating
to upgrade and to install modules. The main reason for this is still a litle confusing
but it as the side effect to log "Unmet dependencies" error multiple time in add_modules,
even if the dependency will be resolved later.

This commit removes the error level for this log, and replace it by another check,
performed at the end, logging any module in "to install"/"to upgrade" state.

Also log removed module as info (25), not warning. This may be changed latter

closes odoo/odoo#43797

X-original-commit: c5d6a3977de85fb974a4940fb11d54ef847e08e4
Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>

Task 1856935

Currently, if installing a module's demo data fails (because the
module was uninstalled and some were left over and can't be
reinstalled, or because they're broken, or…) the installation of the
module fails and further installations are skipped (?).

Since demo data are non-essential (though required to run tests),
rather than fail everything if they fail just roll them back and
notify the user.

This change generates a warning log *and* shows a notification popup
to the end user.

Now that we're closer to switching to P3 for good, these helpers have
outlived their usefulness, and mostly add noise.

All remaining dict.iter*() or dict.view*() must be converted to the
normal keys(), values() or items() calls.

Whenever the result is likely to be used for more than the scope of a
loop, or when the dict needs to be modified during iteration, the calls
must be wrapped in a ``list()``, to protect the new P3 semantics.
Those cases are very exceptional.

Also removed some dead code or improved the API to remove unnecessary
conversions.

In Python 3:

* various builtins and dict methods were changed to return
  view/iterable objects rather than lists
* and the separate Python 2 view/iterable builtins and methods were
  removed altogether

This is problematic when using these items as list (which the happens
repeatedly in Odoo), but more viciously when iterating *multiple times*
over them (which also happens, which I've messed up multiple times while
writing this, and which is a pain to debug even when you've just created
the issue).

Convert all code using these to semantics-matching cross-version
helper functions to get the LCD behaviour between P2 and P3, and
forbid the builtins via lint.

issue #8530

* LDAP import: python-ldap is not python3-compatible, pyldap is

  Warning: only supported from debian Stretch (current testing)?
  https://packages.debian.org/search?searchon=names&keywords=pyldap

* implicitly relative imports
* imports of moved or removed stdlib modules

issue #8530

* Reverse wrapper courtesy of @rco-odoo's original P3 branch
* thin compat module stripped down from werkzeug (to augment as needed)

issue 8530

Demoted to library in Python 3, see if uses can be replaced by more
specific construct, just import functools.reduce otherwise.

Futurize fixers:
* lib2to3.fixes.fix_reduce