test, cmd/evm, core, core/vm: illegal code hash implementation

This implements a generic approach to enabling soft forks by allowing
anyone to put in hashes of contracts that should not be interacted from.
This will help "The DAO" in their endevour to stop any whithdrawals from
any DAO contract by convincing the mining community to accept their code
hash.

core/state/statedb.go

@@ -51,6 +51,8 @@ type StateDB struct {
 	txIndex      int
 	logs         map[common.Hash]vm.Logs
 	logSize      uint
+
+	reducedDao bool
 }
 
 // Create a new state from a given trie
@@ -161,6 +163,14 @@ func (self *StateDB) GetCode(addr common.Address) []byte {
 	return nil
 }
 
+func (self *StateDB) GetCodeHash(addr common.Address) common.Hash {
+	stateObject := self.GetStateObject(addr)
+	if stateObject != nil {
+		return common.BytesToHash(stateObject.codeHash)
+	}
+	return common.Hash{}
+}
+
 func (self *StateDB) GetState(a common.Address, b common.Hash) common.Hash {
 	stateObject := self.GetStateObject(a)
 	if stateObject != nil {