pcap2john.py: improvements for htdigest, gadu, cleanup

[exploide]

Some enhancements for pcap2john.py.

• Rewrote pcap_parser_htdigest function to use scapy for parsing. Prior to this change, it was crashing on pcapng files (as opposed to pcap). Furthermore, it was not compatible with Python 3, now it is. While I was at it, I decided to print Basic Auth credentials directly to stderr. Could be interesting too, but no cracking required. Renamed the function to pcap_parser_http_authorization in this course. Since there was no example file for testing I created https://github.com/openwall/john-samples/pull/26.

• A cleanup commit removes an annoying call to sleep and adds a few comments.

• Accidentally, I discovered pcap_parser_gadu was not compatible with Python 3, now it is. I refactored the function a bit to make it more conformant to the remainder of the script. Tested with the available sample files.

[solardiz]

Thank you very much for your contributions, @exploide!