core, core/vm: added gas price variance table

This implements 1b & 1c of EIP150 by adding a new GasTable which must be
returned from the RuleSet config method. This table is used to determine
the gas prices for the current epoch.

Please note that when the CreateBySuicide gas price is set it is assumed
that we're in the new epoch phase.

In addition this PR will serve as temporary basis while refactorisation
in being done in the EVM64 PR, which will substentially overhaul the gas
price code.

params/gas_table.go

@@ -0,0 +1,65 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package params
+
+import "math/big"
+
+type GasTable struct {
+	ExtcodeSize *big.Int
+	ExtcodeCopy *big.Int
+	Balance     *big.Int
+	SLoad       *big.Int
+	Calls       *big.Int
+	Suicide     *big.Int
+
+	// CreateBySuicide occurs when the
+	// refunded account is one that does
+	// not exist. This logic is similar
+	// to call. May be left nil. Nil means
+	// not charged.
+	CreateBySuicide *big.Int
+}
+
+var (
+	// GasTableHomestead contain the gas prices for
+	// the homestead phase.
+	GasTableHomestead = GasTable{
+		ExtcodeSize: big.NewInt(20),
+		ExtcodeCopy: big.NewInt(20),
+		Balance:     big.NewInt(20),
+		SLoad:       big.NewInt(50),
+		Calls:       big.NewInt(40),
+		Suicide:     big.NewInt(0),
+
+		// explicitly set to nil to indicate
+		// this rule does not apply to homestead.
+		CreateBySuicide: nil,
+	}
+
+	// GasTableHomestead contain the gas re-prices for
+	// the homestead phase.
+	GasTableHomesteadGasRepriceFork = 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),
+
+		CreateBySuicide: big.NewInt(25000),
+	}
+)