Fixup GML-GMLMIP conversion

Variable numbers should not be 0, so shift them by 1 on conversion, then
shift them back.

gmlmip_stub.cc

@@ -47,7 +47,7 @@ static CAMLprim value pair2caml(const int& t) {
     CAMLlocal1( abc );
     abc = caml_alloc(2, 0);
     bool neg = t < 0;
-    Store_field( abc, 0, Val_int(neg ?(-t) : t));
+    Store_field( abc, 0, Val_int((neg ?(-t) : t) - 1));
     Store_field( abc, 1, Val_bool(!neg));
     return abc;
 }
@@ -74,7 +74,7 @@ CAMLprim value gmlRules_stub(value modalities) {
         modvec.push_back(make_pair(make_pair(
             Bool_val(vpos),
             Int_val(vcnt)),
-            Int_val(vformula)));
+            1+Int_val(vformula)));
         block = Field(block, 1);
     }
     // Do one rule step and save result in rulevec