Normalizes bPoint type.

    * **value** must be an string.
    * **value** must be one of the following:

      +--------+
      | corner |
      +--------+
      | curve  |
      +--------+

    * Returned value will be an unencoded ``unicode`` string.

def normalizeBPointType(value):
    """
    Normalizes bPoint type.

    * **value** must be an string.
    * **value** must be one of the following:

      +--------+
      | corner |
      +--------+
      | curve  |
      +--------+

    * Returned value will be an unencoded ``unicode`` string.
    """
    allowedTypes = ['corner', 'curve']
    if not isinstance(value, basestring):
        raise TypeError("bPoint type must be a string, not %s."
                        % type(value).__name__)
    if value not in allowedTypes:
        raise ValueError("bPoint type must be 'corner' or 'curve', not %r."
                         % value)
    return unicode(value)