Revert "Fixes #90 ina  more or less correct fashion."

This reverts commit c59bda4123e7f74312438e46efbc8b4cf738ebed.
Reopen #90 : current solution is absolutly bad, and should not be used.
Was missing for #90 associated test
Fixes #90 the right way : not by using a terrible treeMap, but by using an HashMap in which VertexSet are read to find the best match.
Ensures fix for #90 is really a good thing. In fact, the most annoying part was hidden in findBestRootIn, which was totally wrong : the TreeSet used contained only one item (due to sorting misbehaviour) and the given item was not queried back in set after re-adding it.
By using the right custom for loop, I made sure it was working as expected.