Add tests for uncle timestamps and refactor timestamp type

core/error.go

@@ -25,9 +25,10 @@ import (
 )
 
 var (
-	BlockNumberErr  = errors.New("block number invalid")
-	BlockFutureErr  = errors.New("block time is in the future")
-	BlockEqualTSErr = errors.New("block time stamp equal to previous")
+	BlockNumberErr   = errors.New("block number invalid")
+	BlockFutureErr   = errors.New("block time is in the future")
+	BlockTSTooBigErr = errors.New("block time too big")
+	BlockEqualTSErr  = errors.New("block time stamp equal to previous")
 )
 
 // Parent error. In case a parent is unknown this error will be thrown