- Added new field to dnssec policy structure (SOA serial increment
  policy)
- Removed debug code
- Added some info messages after succcesful signing

Refs #4

- Zones are now automatically (re)signed when server starts/reloads
- Signature validity check now calculates the signature as well - this is used to detect changes to RRs themselves
- 'knotc signzone' issues a force signing of zone - all RRSIGs are dropped and recreated
- Some leaks and bugs still present, but the code is commitable now

Refs #4

refs #103, #4

refs #2137

refs #2137

* Node and rrset now must use new API for changing owner (*_set_owner())
* Every structure that stores pointer to dname must retain reference to it
* Destructors in rrset now release all stored dnames, obsoletes parameters: free_owner
* Destructor in rdata_deep_free has obsolete parameter: free_all_dnames
* Fixed some direct data manipulation
* Some code readability improvements
* To do:
 * Reference counting in zparser is disabled for now, implement correctly.
 * Remove obsolete parameters.
 * Destructors should have no extra parameters.
* Tested with server startup, querying and AXFR client/server

Commit refs #993.

GCC builtins are used for atomic add/sub and fetch.
May be extended with assembly for other compilers later.

Commit refs #993.