support asymmetric FETs and other devices like bipolars that have
three distinct terminals. This does not go as far as it should to
make the array independent of the number of declared terminals of
the device. However, it suffices to make, e.g., parameter "a2=area"
work for a bipolar device, and to generate the right drain and source
areas and perimeters for asymmetric (e.g., extended-drain) devices.
change from passing the HierName to passing the HierContext (of which
HierName is a part) so that more information from HierContext (such
as the cell use being visited) can be passed to the callback
procedure (largely for diagnostic purposes).