core, core/vm, tests: changed the initialisation behaviour of the EVM

The EVM was previously initialised and created for every CALL, CALLCODE,
DELEGATECALL and CREATE. This PR changes this behaviour so that the same
EVM can be used through the session and beyond as long as the
Environment sticks around.

core/vm/runtime/env.go

@@ -41,11 +41,13 @@ type Env struct {
 	logs []vm.StructLog
 
 	getHashFn func(uint64) common.Hash
+
+	evm *vm.Vm
 }
 
 // NewEnv returns a new vm.Environment
 func NewEnv(cfg *Config, state *state.StateDB) vm.Environment {
-	return &Env{
+	env := &Env{
 		state:      state,
 		origin:     cfg.Origin,
 		coinbase:   cfg.Coinbase,
@@ -54,6 +56,9 @@ func NewEnv(cfg *Config, state *state.StateDB) vm.Environment {
 		difficulty: cfg.Difficulty,
 		gasLimit:   cfg.GasLimit,
 	}
+	env.evm = vm.EVM(env)
+
+	return env
 }
 
 func (self *Env) StructLogs() []vm.StructLog {
@@ -64,6 +69,7 @@ func (self *Env) AddStructLog(log vm.StructLog) {
 	self.logs = append(self.logs, log)
 }
 
+func (self *Env) Vm() *vm.Vm               { return self.evm }
 func (self *Env) Origin() common.Address   { return self.origin }
 func (self *Env) BlockNumber() *big.Int    { return self.number }
 func (self *Env) Coinbase() common.Address { return self.coinbase }