20120829
========

- Lino-Welfare:
  Miscellaneous translations.
  Added explicit `blank=True` to ChoiceList fields where necessary.
  
  "jobs.Contract [u'Datumsbereich 01.12.2011...31.12.2011 
  au\xdferhalb Begleitungsperiode 01.08.2012....'] 
  (1 object(s) with primary key 180)"


- Added i18n support (``locale`` dirs) for modules 
  :mod:`lino.modlib.accounts`
  and
  :mod:`lino.modlib.ledger`.
  
- New feature: Lino now supports writing :term:`dummy modules <dummy module>`.
  A little change in :func:`lino.core.modeltools.resolve_app`,
  and a first example `lino.modlib.postings.dummy` 
  used in :mod:`lino_xl.lib.cal`.  
  
- New test application :mod:`lino.test_apps.quantityfield`.

  QuantityFields are implemented as CharFields and 
  therefore should *not* be declared `null=True`. 
  The message 
  `"Nullable CharField %s in %s" % (f.name,model)` 
  produced by  
  :func:`lino.core.kernel.analyze_models`
  is now again a plain Exception.
  
  But if `blank=True`, empty strings are converted to `None` 
  values.
  
  
- `VoucherTypes` caused problems because it had no `blank_item`::

    Exception
    Unresolved value '' for <class 'lino.modlib.ledger.models.VoucherTypes'>
    TRACEBACK:
      File "l:\snapshots\django\django\core\handlers\base.py", line 111, in get_response
        response = callback(request, *callback_args, **callback_kwargs)
      File "l:\snapshots\django\django\views\generic\base.py", line 58, in view
        return self.dispatch(request, *args, **kwargs)
      File "l:\snapshots\django\django\views\generic\base.py", line 79, in dispatch
        return handler(request, *args, **kwargs)
      File "t:\hgwork\lino\lino\ui\extjs3\views.py", line 603, in get
        elem = ar.create_instance()
      File "t:\hgwork\lino\lino\core\actions.py", line 739, in create_instance
        obj = self.actor.create_instance(self,**kw)
      File "t:\hgwork\lino\lino\core\table.py", line 887, in create_instance
        instance = self.model(**kw)
      File "l:\snapshots\django\django\db\models\base.py", line 361, in __init__
        setattr(self, field.attname, val)
      File "l:\snapshots\django\django\db\models\fields\subclassing.py", line 34, in __set__
        obj.__dict__[self.field.name] = self.field.to_python(value)
      File "t:\hgwork\lino\lino\utils\choicelists.py", line 462, in to_python
        return self.choicelist.to_python(value)
      File "t:\hgwork\lino\lino\utils\choicelists.py", line 328, in to_python
        raise Exception("Unresolved value %r for %s" % (value,cls))


  I completely removed the `blank_item` 
  from :class:`ChoiceList <lino.utils.choicelists.ChoiceList>` 
  and replaced it by `None`.
  My feeling (had already been saying before that this `blank_item` was a strange thing).
  But not yet sure whether there will be surprises...