In Anabatic::AntennaProtect, when we cannot insert enough diodes
under a wire cluster. Which makes it likely very long and over an
area where diodes cannot be inserted (chip border close to I/O pads
or over a macro-block). Request extra diode insertion on it's
connecting RoutingPad clusters.

* New: In Anabatic::DiodeCluster, add a "forced diode" counter for
    extra diodes inertions. Only used in the DiodeRps derived class.
* New: In Anabatic::DiodeCluster, add support for a cluster to know
    it's neighbors. Stored as indexes of the table being built in
    Anabatic::antennaProtect(Net*).
* New: In Anabatic::antennaProtect(Net*), when builing the WireCluster,
    also find it's neigbors. Store the index of the cluster a segment
    belongs to in clusterSegments.