7-bit ASCII is not enough to cover corner cases and potentially
harmful qnames.

Change-Id: I83a5af63e7ab3d2ce87c7b5063e55f1a1a6c2e1e

Change-Id: I2a5ed6c68aeee99f13c7e023e148e92e4965b838

Change-Id: I0f1db7e5acd90fa123639a4d8c66765be5882b1d

General idea is regular search with keeping node stack.
If node is found, then return current node.
If node is htable, search for suffixes in htable.
If anything fails, walk up the visited nodes and check if
any visited node has value. If yes, then it is a prefix.

f.e. searching for 'abcd'
visited nodes: root -a-> {1:trie} -b-> {2:htable}
1. search htable for 'cd', 'c'
2. retrace to node {1}, does it have value?
3. yes, node1 is prefix 'ab' for 'abcd'

Change-Id: I622adbe9a127d8317b933af4bf56e1411e2d915f

Change-Id: I429b3833c5db9e78220beb1ea72980b557ba06c4

This allows trie to modify duplicated nodes.

Limitations:
* no dname conversion yet (wrong ordering)
* some traversals won't be implemented (probably won't be needed)
* no index building yet (slow ordered search)

Conflicts:
	src/libknot/zone/zone-tree.c