Be able to set one2many/many2many values in a more convenient way

Fix commited about this:

- my_record.many_ids = [(4, IDS), ...] # As usual, OERP tuples are detected here
- my_record.many_ids = [IDS or records] # Converted to [(6, 0, IDS)]
- my_record.many_ids = [] # [(5,)]
- my_record.many_ids = False # [(5,)]

Support for '+=' and '-=' operators coming soon.

That's done.

With a list of records::

    >>> records = oerp.get('my.model').browse([4, 5])
    >>> my_record.many_ids += list(records)
    >>> [r.id for r in my_record.many_ids]
    [1, 2, 3, 4, 5]

With a list of record IDs::

    >>> my_record.many_ids += [4, 5]
    >>> [r.id for r in my_record.many_ids]
    [1, 2, 3, 4, 5]

With an ID only::

    >>> my_record.many_ids -= 4
    >>> [r.id for r in my_record.many_ids]
    [1, 2, 3, 5]

With a record only::

    >>> record = oerp.get('my.model').browse(5)
    >>> my_record.many_ids -= record
    >>> [r.id for r in my_record.many_ids]
    [1, 2, 3]