Id Picker
----------

The Id picker is a variation on the name chooser that picks numeric
ids when no name is given.

  >>> from zope.app.authentication.idpicker import IdPicker
  >>> IdPicker({}).chooseName('', None)
  u'1'

  >>> IdPicker({'1': 1}).chooseName('', None)
  u'2'

  >>> IdPicker({'2': 1}).chooseName('', None)
  u'1'

  >>> IdPicker({'1': 1}).chooseName('bob', None)
  u'bob'

  >>> IdPicker({'bob': 1}).chooseName('bob', None)
  u'bob1'

