Draft support DNSSEC + DANE

This series of patches adds support for DNSSEC + parsing of DANE structures. This is a draft pull request mostly intended for comments.

Open issues:
1. To add support for sending a query that will set the flags needed by dnssec I had to add ares_create_query2(). Maybe there can be a clever way to avoid introducing another create query function, but I couldn't think of any.

2. How to determine the servers to use when dnssec is requested. Currently it uses an extension of resolv.conf (the trusted-nameserver line), as proposed in:
https://www.sourceware.org/ml/libc-alpha/2014-06/msg00307.html

3. I'm not so experienced with DNS and its terminology. A review by someone who is more familiar may help.