error when an m2m field is updated by an onchange

[Christophe Combelles]

This bug only appears in the web client, just like #906449.

- Create a view (in our case a wizard) with two fields, the second one being a many2many.
- In an onchange callback on the first field, return something that will update the many2many field (something like { 'value': [1, 2, 3] }).
- When you validate the view or wizard, the server receives [(1, 2, 3)] instead of [1, 2, 3] and fails on a SQL request.

The error shows up in the server log as :
LIGNE 1 : ....id FROM "account_period" WHERE account_period.id IN ((1, 2,...
The SQL request should rather be :
 ....id FROM "account_period" WHERE account_period.id IN (1, 2,...

==> After hours of digging, we found the error here :
webclient/addons/openerp/widgets/listgrid.py : 173

        if ids and not isinstance(ids, list):
            ids = [ids]

It should rather be:

        if ids and not isinstance(ids, (list, tuple)):
            ids = [ids]

For any reason, the [1, 2, 3] list coming from the server is converted to a tuple, when it reaches the web client. The web client then wraps it in a list and at the end ids = [(1, 2, 3)] instead of [1, 2, 3].