Add the remaining comparisons for icmp.

stepper.py

@@ -155,6 +155,14 @@ def eval_icmp(cnd, left, right):
         return left == right
     elif cnd == 'ne':
         return left != right
+    elif cnd == 'slt':
+        return left < right
+    elif cnd == 'sle':
+        return left <= right
+    elif cnd == 'sgt':
+        return left > right
+    elif cnd == 'sge':
+        return left >= right
     else:
         err('eval_icmp: Unknown cnd: {}'
             .format(cnd))