Missing RCU unlock + replaced numbers by error codes.

cov#10633 cov#10634

refs #1976

refs #1976

refs #1976

refs #1976

refs #1976

Added some missing read locks.
TODO: may deadlock somewhere, some functions still find zone from zonedb
and may corrupt new reloaded zone instead of zone the transfer was started

refs #1976

refs #1976

- Actual RDATA of zone were beeing changed due to improper API usage.

Refs #1965

- Missing NSEC/NSEC3 is no longer considered an error.

refs #1970

refs #1950

- If a node contains a CNAME RRSet or just a RRSIG covering a
  CNAME, the server will not try to resolve the CNAE chain.

refs #1971

This option allows binding to the same port using separate
IPv6 and IPv4 socket.

refs #1877

refs #1877

- Freeing RRSIGs after RRSet deep copy (there's no switch that would mean no RRSIGs copyiing)
- Added assert to zone-dump that checks for such state

Refs #1752

refs #1968

refs #1969

- Added to zones section (configuration reference), might be moved later

Refs #1877 @2h

- Was causing compilation error with latest OpenSSL (v1.0.1C)
- Made rdata conversion functions static.

- Disabled where I was able to tell it's OK.
- Enabled in zone-diff, as I'm not sure it would work without it.

Should mitigate problems with IXFRs.

Conflicts:
	src/libknot/updates/xfr-in.c

- Wrong flag was used.
- Added some detailed debug messages (may be removed later).

refs #1952 @3h