core, core/state, trie: EIP158, reprice & skip empty account write

This commit implements EIP158 part 1, 2, 3 & 4

1. If an account is empty it's no longer written to the trie. An empty
  account is defined as (balance=0, nonce=0, storage=0, code=0).
2. Delete an empty account if it's touched
3. An empty account is redefined as either non-existent or empty.
4. Zero value calls and zero value suicides no longer consume the 25k
  reation costs.

params: moved core/config to params

Signed-off-by: Jeffrey Wilcke <jeffrey@ethereum.org>

light/txpool.go

@@ -28,6 +28,7 @@ import (
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/logger"
 	"github.com/ethereum/go-ethereum/logger/glog"
+	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
 	"golang.org/x/net/context"
 )
@@ -42,7 +43,7 @@ var txPermanent = uint64(500)
 // always receive all locally signed transactions in the same order as they are
 // created.
 type TxPool struct {
-	config   *core.ChainConfig
+	config   *params.ChainConfig
 	quit     chan bool
 	eventMux *event.TypeMux
 	events   event.Subscription
@@ -76,7 +77,7 @@ type TxRelayBackend interface {
 }
 
 // NewTxPool creates a new light transaction pool
-func NewTxPool(config *core.ChainConfig, eventMux *event.TypeMux, chain *LightChain, relay TxRelayBackend) *TxPool {
+func NewTxPool(config *params.ChainConfig, eventMux *event.TypeMux, chain *LightChain, relay TxRelayBackend) *TxPool {
 	pool := &TxPool{
 		config:   config,
 		nonce:    make(map[common.Address]uint64),