Ddns When Zone Is Reloaded

See the commit message.

Update .travis.yml to not depend on build-dep command since Travis CI servers don't know knot package (yet)

- server_reconfigure before 'log_update_privileges', note added
- no introductory 'parsing configuration...' line
- logging starts right after the config is parsed, note added

`interface ADDRESS IPA6 '@' NUM` had AF_INET family

- NSs in apex - some possibly problematic scenarios.
- CNAMEs - dtto

refs !205

No Default Nsec3 Tree

Two parts:

* Growable hash node size in trie
* NSEC3 tree created only if needed (NULL is treated as an empty tree)
  * I'm not sure if I did the zone-diff stuff right? :suspect:

http://www.ucw.cz/gitweb/?p=libucw.git;a=blob;f=ucw/bigalloc.c;hb=HEAD

Leaf hhash node size is growable (1-4 pages).
The rule is simple, when a hashtable is split the left and right
children size is clamped left and right weight to the nearest
hhash size. The sizes are chosen arbitrarily so the table size
is always a multiple of page size.

Don't merge RRs in the incoming packets

- misleading statement
- module name in heading
- s/forward\./example./g

Both master and slave scenarios. Master should fail, slave should
load the zone.

Later, log messages should be checked too, but that's not possible now.