Ignore replayed commands on the metastore.

This commit changes the metastore to ignore any commands that are replayed
against it. This is typically handled by the messaging.Conn but there's no
sense in panicing in the metastore if a replayed message comes through.

metastore.go

@@ -76,8 +76,11 @@ func (m *metastore) mustView(fn func(*metatx) error) (err error) {
 // Panics if a disk or system error occurs. Return error from the fn for validation errors.
 func (m *metastore) mustUpdate(index uint64, fn func(*metatx) error) (err error) {
 	if e := m.update(func(tx *metatx) error {
+		// Ignore replayed commands.
 		curr := tx.index()
-		assert(index == 0 || index > curr, "metastore index replay: meta=%d, index=%d", curr, index)
+		if index > 0 && index <= curr {
+			return nil
+		}
 
 		// Execute function passed in.
 		err = fn(tx)