check for illegal DEVsetup() DEVunsetup() patterns.

Consider the following silent contracts:
1)
 CKTsetup() invocations must be separated by a CKTunsetup() invocation
 But CKTsetup() has an internal flag,
   which will prevent re-invocation of DEVsetup()
 But DEVsetup() will be called during sensitivity analysis,
   bypassing this precaution. It is fatal if this will
   cause another node allocation (CKTmk..()).
   This commit tries to detect such cases.
   (Note: many DEVsetup routines (all ?) have their CKTmk..() invocations
      guarded to avoid reallocation of local nodes,
      see commit f7f454c0a1
        bug fix, fix the guard for device generated internal nodes (via CKTmkVolt())
   )
   FIXME:
     DEVsetup() is seriously obfuscated by these guards.
     If would be far better, if the sensitivity analysis
       wouldn't sidestep into DEVsetup()
     consider a device local variant of the CKTisSetup flag
2)
 DEVunsetup() must delete all, each and every,
   local allocated node in DEVsetup()
 Otherwise CKTmk..() invocations in a following CKTsetup() will
   return duplicate node numbers, effectively shorting device nodes.
 This commit tries to detect incomplete CKTdltNNum() invocations.
3)
  DEVunsetup() must not delete a netlist node.
  This can easily happen in those devices which have optional ports,
    which have code in DEVsetup() which copies node numbers to
    local node variables.
  This commit tries to detect such errors.

src/include/ngspice/cktdefs.h

@@ -152,6 +152,7 @@ struct CKTcircuit {
 
     CKTnode *CKTnodes;          /* ??? */
     CKTnode *CKTlastNode;       /* ??? */
+    CKTnode *prev_CKTlastNode;  /* just before model setup */
 
     /* This define should be somewhere else ??? */
 #define NODENAME(ckt,nodenum) CKTnodName(ckt,nodenum)

src/spicelib/analysis/cktdltn.c

@@ -23,6 +23,11 @@ CKTdltNNum(CKTcircuit *ckt, int num)
     CKTnode *n, *prev, *node, *sprev;
     int	error;
 
+    if (!ckt->prev_CKTlastNode->number || num <= ckt->prev_CKTlastNode->number) {
+        fprintf(stderr, "Internal Error: CKTdltNNum() removing a non device-local node, this will cause serious problems, please report this issue !\n");
+        controlled_exit(EXIT_FAILURE);
+    }
+
     prev  = NULL;
     node  = NULL;
     sprev = NULL;

src/spicelib/analysis/cktsens.c

@@ -364,10 +364,15 @@ int sens_sens(CKTcircuit *ckt, int restart)
 			ckt->CKTnumStates = sg->istate;
 
 			fn = DEVices[sg->dev]->DEVsetup;
-			if (fn)
-				fn (delta_Y, sg->model, ckt,
-					/* XXXX insert old state base here ?? */
-					&ckt->CKTnumStates);
+			if (fn) {
+                            CKTnode *n = ckt->CKTlastNode;
+                            /* XXXX insert old state base here ?? */
+                            fn (delta_Y, sg->model, ckt, &ckt->CKTnumStates);
+                            if (n != ckt->CKTlastNode) {
+                                fprintf(stderr, "Internal Error: node allocation in DEVsetup() during sensitivity analysis, this will cause serious troubles !, please report this issue !\n");
+                                controlled_exit(EXIT_FAILURE);
+                            }
+                        }
 
 			/* ? CKTsetup would call NIreinit instead */
 			ckt->CKTniState = NISHOULDREORDER | NIACSHOULDREORDER;

src/spicelib/analysis/cktsetup.c

@@ -77,6 +77,13 @@ CKTsetup(CKTcircuit *ckt)
     SetAnalyse("Device Setup", 0);
 #endif
 
+    /* preserve CKTlastNode before invoking DEVsetup()
+     * so we can check for incomplete CKTdltNNum() invocations
+     * during DEVunsetup() causing an erronous circuit matrix
+     *   when reinvoking CKTsetup()
+     */
+    ckt->prev_CKTlastNode = ckt->CKTlastNode;
+
     for (i=0;i<DEVmaxnum;i++) {
         if ( DEVices[i] && DEVices[i]->DEVsetup && ckt->CKThead[i] ) {
             error = DEVices[i]->DEVsetup (matrix, ckt->CKThead[i], ckt,
@@ -163,6 +170,13 @@ CKTunsetup(CKTcircuit *ckt)
                 error = e2;
         }
     }
+
+    if (ckt->prev_CKTlastNode != ckt->CKTlastNode) {
+        fprintf(stderr, "Internal Error: incomplete CKTunsetup(), this will cause serious problems, please report this issue !\n");
+        controlled_exit(EXIT_FAILURE);
+    }
+    ckt->prev_CKTlastNode = NULL;
+
     ckt->CKTisSetup = 0;
     if(error) return(error);