Abstract pins are created when pins are not attached to any or only to passive nets
(passive nets are those without device terminals or subcircuit pins).
1. Such pins were treated swappable. Now named pins will not be treated
swappable but are mapped by name. This enables blackbox models where
the pins are labelled and must correspond to schematic pins.
2. A bug was present which lead to incorrect handling of abstract
nets in net compare.