* Change: In Etesian::SubSlice::getUsedVTracks(), now take blockages
into account for used vertical tracks.
* Bug: In Etesian::SubSlice::avoidTrack(), right free interval for
shifting was wrongly computed, effectively allowing *any* shift.
This was creating cells overlap!
* New: In Hurricane::BasicLayer & Layer, establish a two way link
between the blockage layer and routing layer. Now we can access
the routing layer from the blockage.