[FIX] fields: when executing (4, *) operations on o2m fields, check the existence based on the sql model of the table.

If the o2m field linked to the o2m is stored on a different table (eg: inherit), previous request would crash as the field do not exists in the '_table' sql table
[FIX] parent_model is null if local column
[FIX] fields: when executing (4, *) operations on o2m fields, check the existence based on the sql model of the table.

If the o2m field linked to the o2m is stored on a different table (eg: model with _inherit), previous request would crash as the field do not exists in the '_table' sql table
[IMP] cookies: when retrieving session cookie, catch eventual errors and remove malformed cookie
[IMP] cookies: when retrieving session cookie, catch eventual parsing errors and remove cookie if incorrect (opw 605648)

In case of unparsable cookie (modified, corrupted,...), openerp would not load and crash with white screen until expiration.
With the fix goes back to login screen.
Merge branch 'bzr/openobject-server-7.0'
Merge branch 'bzr/openerp-web-7.0'