chainntnfs/btcdnotify: properly include SpendingHeight in SpendDetails

This commit modifies the btcdnotify implementation of the ChainNotifier
interface to properly include the height in which the watched output
was spent in the SpendDetail sent as a notification.

The set of tests have also been updated to assert that the proper
spending height is included in received notification.

chainntnfs/btcdnotify/btcd.go

@@ -369,15 +369,22 @@ out:
 				// the notification subscriber.
 				if clients, ok := b.spendNotifications[prevOut]; ok {
 					spenderSha := newSpend.tx.Hash()
-					for _, ntfn := range clients {
-						spendDetails := &chainntnfs.SpendDetail{
-							SpentOutPoint: ntfn.targetOutpoint,
-							SpenderTxHash: spenderSha,
-							// TODO(roasbeef): copy tx?
-							SpendingTx:        spendingTx.MsgTx(),
-							SpenderInputIndex: uint32(i),
-						}
+					spendDetails := &chainntnfs.SpendDetail{
+						SpentOutPoint:     &prevOut,
+						SpenderTxHash:     spenderSha,
+						SpendingTx:        spendingTx.MsgTx(),
+						SpenderInputIndex: uint32(i),
+					}
+					// TODO(roasbeef): after change to
+					// loadfilter, only notify on block
+					// inclusion?
+					if newSpend.details != nil {
+						spendDetails.SpendingHeight = newSpend.details.Height
+					} else {
+						spendDetails.SpendingHeight = currentHeight
+					}
 
+					for _, ntfn := range clients {
 						chainntnfs.Log.Infof("Dispatching "+
 							"spend notification for "+
 							"outpoint=%v", ntfn.targetOutpoint)