Also removed some unused code.

ref #121

ref #121

ref #121

ref #121

Since inserting into hashtable may fail, this would result in lost
records. I refactored the code a bit and hashtable node split is now
done recursively, i.e. it divides nodes until it fits.

Sorted iteration is not needed and hhash doesn't support sorted
iteration unless an order index is built.

Use pointer-based thread identifiers instead of number-based ones. This
should resolve compilation warnings on BSD systems.

Linux uses integers as thread identifiers, BSD based systems use pointers.

ref #157

Conflicts:
	src/knot/server/tcp-handler.c

(just for testing, will be refactored)

IXFR SOA response implemented.