Adds the given values to the given feature.

def extend (name, values):
    """ Adds the given values to the given feature.
    """
    assert isinstance(name, basestring)
    assert is_iterable_typed(values, basestring)
    name = add_grist (name)
    __validate_feature (name)
    feature = __all_features [name]

    if feature.implicit:
        for v in values:
            if v in __implicit_features:
                raise BaseException ("'%s' is already associated with the feature '%s'" % (v, __implicit_features [v]))

            __implicit_features[v] = feature

    if values and not feature.values and not(feature.free or feature.optional):
        # This is the first value specified for this feature,
        # take it as default value
        feature.set_default(values[0])

    feature.add_values(values)