7.21 Page 194 -- typographical error in register_decoder function

[samkramer]

Original version -- attempting to access mimetype attribute of string object:

def register_decoder(cls):
	for mt in cls.mimetypes:
		_registry[mt.mimetype] = cls
	return cls

Fixed version:

def register_decoder(cls):
    for mt in cls.mimetypes:
        _registry[mt] = cls
    return cls