The tranif input pins are normally nothing special, but sometimes
they are fed back from the switch body. In this case, the control
needs to see the current *output* from the fed back port, in order
to get the results that people expect.
Two bugs:
(1) propagating values through the branch accidentally also
did a part select.
(2) Not all nodes of the branch nexus didn't receive a calculated
values, even though they were all marked as done.
In the process, I cleaned up the code a bit, and documented it for
better understanding.
Tran islands are a kinds of island, so seperate the tran handling
from the core island concept. This will allow for creating new
kinds of islands. (Think analog.)
Stephen Williams