Fix issues with deprecated cache

lib/hk-util.js

@@ -438,13 +438,12 @@ const getHistoryOffset = (Env, channelName, lastKnownHash, _cb) => {
                     to reconcile their differences. */
             }
 
-            // If our lastKnownHash is older than the 2nd to last checkpoint,
-            // only send the last 2 checkpoints and ignore "lkh"
-            // XXX XXX this is probably wrong! ChainPad may not accept checkpoints that are not connected to root
-            // XXX We probably need to send an EUNKNOWN here so that the client can recreate a new chainpad
-            /*if (lkh && index.cpIndex.length >= 2 && lkh < index.cpIndex[0].offset) {
-                return void cb(null, index.cpIndex[0].offset);
-            }*/
+            // If our lastKnownHash is older than the 2nd to last checkpoint, send
+            // EUNKNOWN to tell the user to empty their cache
+            if (lkh && index.cpIndex.length >= 2 && lkh < index.cpIndex[0].offset) {
+                waitFor.abort();
+                return void cb(new Error('EUNKNOWN'));
+            }
 
             // Otherwise use our lastKnownHash
             cb(null, lkh);