After we have first seen the hop for a final destination, ignore hops with the
same target which come afterward (have bigger hop number).
Correctly handle hops for which we never got a response back.
Update affected tests.
Be consistent with 'traceroute' and use 1-based hop numbers.
Use more strict asserts.
Merge pull request #3 from Kami/remove_duplicated_results

Ignore duplicated hops and correctly handle hops which never return a response