Add another error qualifier to decribe the current policy

when a doubling token exists (or is created) in the netlist.

src/include/ngspice/iferrmsg.h

@@ -34,7 +34,8 @@ Author: 1986 Thomas L. Quarles
 #define E_NOCHANGE 13   /* simulator can't tolerate any more topology changes */
 #define E_NOTFOUND 14   /* simulator can't find something it was looking for */
 #define E_BAD_DOMAIN 15 /* output interface begin/end domain calls mismatched */
-
+#define E_EXISTS_BAD 16 /* error - attempt to create duplicate */
+                        /* instance or model. Bail out. */
 
 #define E_PRIVATE 100   /* messages above this number are private to */
                         /* the simulator and MUST be accompanied by */

src/spicelib/devices/cktcrte.c

@@ -32,7 +32,7 @@ CKTcrtElt(CKTcircuit *ckt, GENmodel *modPtr, GENinstance **inInstPtr, IFuid name
     if (instPtr) { 
         if (inInstPtr)
 	    *inInstPtr = instPtr;
-        return E_EXISTS;
+        return E_EXISTS_BAD;
     }
 
     type = modPtr->GENmodType;

src/spicelib/parser/sperror.c

@@ -29,7 +29,10 @@ const char *SPerror(int type)
     case E_EXISTS:
 	msg = "device already exists, existing one being used";
 	break;
-    case E_NODEV:
+    case E_EXISTS_BAD:
+	msg = "device already exists, bail out";
+	break;
+	case E_NODEV:
 	msg = "no such device";
 	break;
     case E_NOMOD: