Get an iterator to one past the end element in a buffer sequence.

template<
    typename ConvertibleToBuffer>
const ConvertibleToBuffer * buffer_sequence_end(
    const ConvertibleToBuffer & b,
    constraint_t< !is_convertible< const ConvertibleToBuffer *, const mutable_buffer * >::value >  = 0,
    constraint_t< !is_convertible< const ConvertibleToBuffer *, const const_buffer * >::value >  = 0,
    constraint_t< is_convertible< ConvertibleToBuffer, mutable_buffer >::value||is_convertible< ConvertibleToBuffer, const_buffer >::value >  = 0);