core, core/state, trie: Hardfork EIP155, EIP161, EIP170

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>

params/gas_table.go

@@ -26,6 +26,8 @@ type GasTable struct {
 	Calls       *big.Int
 	Suicide     *big.Int
 
+	ExpByte *big.Int
+
 	// CreateBySuicide occurs when the
 	// refunded account is one that does
 	// not exist. This logic is similar
@@ -44,6 +46,7 @@ var (
 		SLoad:       big.NewInt(50),
 		Calls:       big.NewInt(40),
 		Suicide:     big.NewInt(0),
+		ExpByte:     big.NewInt(10),
 
 		// explicitly set to nil to indicate
 		// this rule does not apply to homestead.
@@ -52,6 +55,8 @@ var (
 
 	// GasTableHomestead contain the gas re-prices for
 	// the homestead phase.
+	//
+	// TODO rename to GasTableEIP150
 	GasTableHomesteadGasRepriceFork = GasTable{
 		ExtcodeSize: big.NewInt(700),
 		ExtcodeCopy: big.NewInt(700),
@@ -59,6 +64,19 @@ var (
 		SLoad:       big.NewInt(200),
 		Calls:       big.NewInt(700),
 		Suicide:     big.NewInt(5000),
+		ExpByte:     big.NewInt(10),
+
+		CreateBySuicide: big.NewInt(25000),
+	}
+
+	GasTableEIP158 = GasTable{
+		ExtcodeSize: big.NewInt(700),
+		ExtcodeCopy: big.NewInt(700),
+		Balance:     big.NewInt(400),
+		SLoad:       big.NewInt(200),
+		Calls:       big.NewInt(700),
+		Suicide:     big.NewInt(5000),
+		ExpByte:     big.NewInt(50),
 
 		CreateBySuicide: big.NewInt(25000),
 	}