Improve speed for Record instanciation and group clear

[yangoon1, 2010-08-24 00:47:23]

New DB on neso, on opening of initial company wizard:

Traceback (most recent call last):
  File "/tryton/gui/window/view_form/view/form.py", line 99, in _sig_clicked
    return self._action(action, atype)
  File "/tryton/gui/window/view_form/view/form.py", line 144, in _action
    value = Action._exec_action(act, self.window, data, {})
  File "/tryton/action/main.py", line 169, in _exec_action
    email=action.get('email'), context=context)
  File "/tryton/wizard/main.py", line 227, in execute
    context=ctx)
  File "/tryton/action/main.py", line 169, in _exec_action
    email=action.get('email'), context=context)
  File "/tryton/wizard/main.py", line 227, in execute
    context=ctx)
  File "/tryton/action/main.py", line 169, in _exec_action
    email=action.get('email'), context=context)
  File "/tryton/wizard/main.py", line 213, in execute
    size=res['size'], context=ctx)
  File "/tryton/wizard/main.py", line 58, in __init__
    self.screen.add_view(arch, fields, display=True)
  File "/tryton/gui/window/view_form/screen/screen.py", line 368, in add_view
    self.new()
  File "/tryton/gui/window/view_form/screen/screen.py", line 404, in new
    record = self.group.new(default, self.domain, ctx)
  File "/tryton/gui/window/view_form/model/group.py", line 242, in new
    record.default_get(domain, ctx)
  File "/tryton/gui/window/view_form/model/record.py", line 232, in default_get
    self.set_default(vals)
  File "/tryton/gui/window/view_form/model/record.py", line 298, in set_default
    modified=modified)
  File "/tryton/gui/window/view_form/model/field.py", line 459, in set_default
    group.record_deleted.extend(x for x in record.value[self.name]
KeyError: 'addresses'

[yangoon1, 2010-08-26 10:22:32]

It is difficult for me to see the speed improvement, at least the client is not
slower. So this patch works for me.