Implemented a new check for the KCL Verification, based on the maximum of the unknown current branches at each voltage node.

Please note that this check introduces the theoretically correct check, but, since achieving this target involves the perfect knowledge of every model,
 we can use this suboptimal and practical check (to be extended with the other possible unknown current branches)

src/spicelib/analysis/cktmkcurKCL.c

@@ -0,0 +1,21 @@
+/**********
+Author: 2013 Francesco Lannutti
+**********/
+
+#include "ngspice/ngspice.h"
+#include "ngspice/sperror.h"
+#include "ngspice/cktdefs.h"
+
+int
+CKTmkCurKCL (CKTcircuit *ckt, int i, double **node)
+{
+    CKTmkCurKCLnode *tempNode ;
+
+    tempNode = TMALLOC (CKTmkCurKCLnode, 1) ;
+    tempNode->KCLcurrent = 0.0 ;
+    tempNode->next = ckt->CKTmkCurKCLarray [i] ;
+    ckt->CKTmkCurKCLarray [i] = tempNode ;
+    *node = &(tempNode->KCLcurrent) ;
+
+    return (OK) ;
+}

src/spicelib/devices/ind/indnode.c

@@ -0,0 +1,29 @@
+/**********
+Author: 2013 Francesco Lannutti
+**********/
+
+#include "ngspice/ngspice.h"
+#include "ngspice/cktdefs.h"
+#include "inddefs.h"
+#include "ngspice/sperror.h"
+
+int
+INDnodeIsNonLinear (GENmodel *inModel, CKTcircuit *ckt)
+{
+    INDmodel *model = (INDmodel *)inModel ;
+    INDinstance *here ;
+    int error ;
+
+    /* loop through all the IND models */
+    for ( ; model != NULL ; model = model->INDnextModel)
+    {
+        /* loop through all the instances of the model */
+        for (here = model->INDinstances ; here != NULL ; here = here->INDnextInstance)
+        {
+            error = CKTmkCurKCL (ckt, here->INDposNode, &(here->KCLcurrentPos)) ;
+            error = CKTmkCurKCL (ckt, here->INDnegNode, &(here->KCLcurrentNeg)) ;
+        }
+    }
+
+    return (OK) ;
+}

src/spicelib/devices/vsrc/vsrcnode.c

@@ -0,0 +1,29 @@
+/**********
+Author: 2013 Francesco Lannutti
+**********/
+
+#include "ngspice/ngspice.h"
+#include "ngspice/cktdefs.h"
+#include "vsrcdefs.h"
+#include "ngspice/sperror.h"
+
+int
+VSRCnodeIsNonLinear (GENmodel *inModel, CKTcircuit *ckt)
+{
+    VSRCmodel *model = (VSRCmodel *)inModel ;
+    VSRCinstance *here ;
+    int error ;
+
+    /* loop through all the VSRC models */
+    for ( ; model != NULL ; model = model->VSRCnextModel)
+    {
+        /* loop through all the instances of the model */
+        for (here = model->VSRCinstances ; here != NULL ; here = here->VSRCnextInstance)
+        {
+            error = CKTmkCurKCL (ckt, here->VSRCposNode, &(here->KCLcurrentPos)) ;
+            error = CKTmkCurKCL (ckt, here->VSRCnegNode, &(here->KCLcurrentNeg)) ;
+        }
+    }
+
+    return (OK) ;
+}