all types specified in the "substrate" statement, split such types
into those on the declared well plane, and everything else. Any
types on the well plane are searched as before. Types not on the
well plane (e.g., psd on active) are searched and added to the
substrate node *only* if overlapping nothing on the well plane.
This allows a type such as "psd" to be used on, e.g., both space
(substrate) and deep pwell, but only be extracted as part of the
substrate when found over space. Note that if there is NO
implicit substrate, the substrate connections will always be
found through the usual connection rules.
Tim Edwards
942eaf8113