refs #137

Problem was the function is copied from another one which
always decrements the arcount and trims the TSIG RR. But with
aggregated responses, this should be stripped not from first,
but from the packet actually containing the TSIG.

refs #122

refs #118

refs #118

Either set it to 0 or comment out the statement.

Main changes:
* 'system.hostname' config option is deprecated
* 'system.identity' is used for 'id.server' and 'hostname.bind'
* 'system.version' is used for 'version.server' and 'version.bind'
* In addition, config options (and NSID) support boolean on|off
* When on, the automatic default is filled on config load:
  * FQDN hostname (or at least hostname) for NSID and system.identity
  * Version string for system.version

The config options are still turned off by default.
refs #113

There was also a small error when a TCP master socket was removed,
the next one was skipped regardless of it's activity level.

If previous xfer socket was disconnected, the 'ret' variable wasn't cleared
when the current socket is inactive. The outcome of this is that the
innocent transfer could be discarded.

Thanks to Jonathan Hoppe from Netriplex for discovering this.

refs #111

* xfrin_add_new_node and ddns_add_new_node were duplicates
  - knot_node_set_zone() was called in the _add functions anyway
* merged checks for NSEC3-related RR to knot_rrset_is_nsec3rel()
  - the empty RR check was pointless, as even if empty, the node
    shouldn't be searched in normal tree

Refs #102

     - Inserting DNAMEs from out-of-zone RRs into tmp DNAME table messed
things up when we free'd the RRSet, it's better to check before
inserting into table (one could rollback the table, but there are some
corner cases not worth solving)

Refs #102

refs #100