(asn1_der_iterator_init): Initialize length and

data.
(asn1_der_iterator_next): Support for lengths >= 0x80.
(asn1_der_decode_constructed_last, asn1_der_decode_bitstring)
(asn1_der_decode_bitstring_last): New functions.
(asn1_der_get_bignum): Check for non-mininal encodings.

Rev: src/nettle/der-iterator.c:1.2