dao: put contract IDs into keys using big endianness

We don't have a need to iterate over them at the moment, but since we're
changing the DB format in the next release anyway let's add this ability also,
just in case.

pkg/core/blockchain.go

@@ -46,7 +46,7 @@ import (
 // Tuning parameters.
 const (
 	headerBatchCount = 2000
-	version          = "0.2.4"
+	version          = "0.2.5"
 
 	defaultInitialGAS                      = 52000000_00000000
 	defaultGCPeriod                        = 10000

pkg/core/dao/dao.go

@@ -99,7 +99,7 @@ func (dao *Simple) putWithBuffer(entity io.Serializable, key []byte, buf *io.Buf
 func (dao *Simple) makeContractIDKey(id int32) []byte {
 	key := dao.getKeyBuf(5)
 	key[0] = byte(storage.STContractID)
-	binary.LittleEndian.PutUint32(key[1:], uint32(id))
+	binary.BigEndian.PutUint32(key[1:], uint32(id))
 	return key
 }