This prevents mixing up the current IXFR and started AXFR.

Change-Id: Ia44220989918f9eb53b3f2a2b1d74b092aef4246

Change-Id: I760f21c2dc4823c6b1c014c629f30c55827ee094

reffs #36

refs #36

refs #36

refs #36

AF_UNIX is now preferred over AF_INET sockets, although it is still
off by default.
When TCP/IP is used, default port changed from 5553->5533 (free).
AF_UNIX socket based control doesn't use (naturally) 'allow' section.

refs #36

refs #36

It is still possible to control knotd using signals though,
but the 'knotc' will use just the one configured channel not a mix
of signals and channel.

refs #36

Removed 'pidfile' config option in favour of 'rundir' for later
storage of UNIX sockets and other stuff.
Default of 'rundir' is $(localstatedir)/run/knot
Default of 'storage' is $(sharedstatedir)/knot

refs #36

- Removed functions from zone-contents - no need for them to be public.

- Mimics BIND

Two reasons:
- There's some rare race condition in the queue implementation
- Doesn't scale and current performance is almost the same (-~2%)
- Created branch with the queue still retained for future inspection

This should be properly solved by better zone fetching API with
a) refcounting b) locking.

refs #31
fixes #30