- Semantic check: missing conversion of next NSEC to lowercase
  when comparing with apex.
- Changed condition when SERVFAIL is returned (no combination
  with any possible Ext RCODE).

Only RFC 4034 types are converted to lowercase.
Unified the conversion to one RRSet function used in both zone
parsing and packet parsing.

Also refactored a bit.
TODO: Remove the use of parse_rdata() function in utilities, so
      that it may become static.

Bad source size counting. Still needs polishing.

Used traverse_rdata() function. Still needs some polising and
more refactoring (together with the rr_from_wire() function.

First draft. Requires some optimizations and testing.

Fixes unexpanded wildcard appearance in Additional section.

- includes not finished yet

- Fixed DO flag setting.
- Fixed RDATA setting in OPT init. There was some weird problem
  with the allocated dummy RDATA. Using stack instead.
- Flags were not initialized.
- Fixed flag setting in kdig.

- OPT RR is now a normal RRSet.
- Server stores only some EDNS options.
  (Will be changed later back to whole RR.)
- Rewritten EDNS getters and setters to use normal RRSet.
  (Option manipulation not done yet.)
- Added helper function for getting RRSet TTL.