[FIX] base: access to preferences menu for portal users

Since revs 53582c2ea6 & f65c913027,
this was no more possible for portal users to read groups
on purpose, for privacy reasons.

fields_get of res.users model is overriden, for
the access rights form view features
(The groups selections and checkboxes).
At each call to fields_get, which happens at each call
to fields_view_get on the res.users model, operations are
done on the model res.groups (basically, to
build the selection groups and checkboxes). So,
each time a view of model res.users is displayed,
whatever the view, operations on res.group model were performed.

The thing is, these operations on res.groups
are actually needed only for the user access rights
view, or at least only for users having the group
Administration > Access rights. These group operations
aren't needed for the preferences view, nor for portal users.

We therefore avoid to do these if the user is not part of the
Administration > Access rights group, which lead to
performances improvment, and solves the fact
portal users couldn't access their user preferences view.

opw-627391

openerp/addons/base/res/res_users.py

@@ -860,6 +860,8 @@ class users_view(osv.osv):
     def fields_get(self, cr, uid, allfields=None, context=None, write_access=True):
         res = super(users_view, self).fields_get(cr, uid, allfields, context, write_access)
         # add reified groups fields
+        if uid != SUPERUSER_ID and not self.pool['res.users'].has_group(cr, uid, 'base.group_erp_manager'):
+            return res
         for app, kind, gs in self.pool.get('res.groups').get_groups_by_application(cr, uid, context):
             if kind == 'selection':
                 # selection group field