Add KNOWNBUG test for SMV ranges

Author: kroening

regression/ebmc/range_type/range_type6.desc

@@ -0,0 +1,8 @@
+KNOWNBUG
+range_type6.smv
+--bound 10
+^EXIT=0$
+^SIGNAL=0$
+--
+--
+The result does not match the expected result.

regression/ebmc/range_type/range_type6.smv

@@ -0,0 +1,14 @@
+MODULE main
+VAR x:1..6;
+
+ASSIGN
+  init(x) := 1;
+
+  next(x) :=
+    case
+      x=1 : x+1;
+      TRUE: 4;
+    esac;
+
+-- should fail
+LTLSPEC G x!=4