Allow to register a callback function in the cfunc.mod files,
which will be invoked in MIFdestroy.
Usefull to "free" memory which has been allocated locally in a cfunc.mod file.
src/spicelib/devices/*/*set.c, XXXunsetup(), reset local node variables unconditionally
and use a more robust test for local node numbers.
That is, transform this pattern :
if (here->Node && ...) {
CKTdltNNum(ckt, here->Node);
here->Node = 0;
}
into this :
if (here->Node > 0 && ...)
CKTdltNNum(ckt, here->Node);
here->Node = 0;
The change of "!= 0" ==> "> 0" accounts for rare cases where "Node"
might have been set to -1, (meaning "unconnected")
The unconditional execution of the zero assignment is for those cases
where "Node" might have been assigned to some external or other local Node.
If so, the variable would not be set to zero, confusing the "guarding" if's
in the corresponding XXXsetup() routine.
The Pattern to follow is:
1) unset and delete *all* local Nodes in XXXunsetup()
2) allocate all of them again in a re-invocation of XXXsetup(),
exactly the same way as in the very first invocation.
