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>

core/dao.go

@@ -33,7 +33,7 @@ import (
 //      with the fork specific extra-data set
 //   b) if the node is pro-fork, require blocks in the specific range to have the
 //      unique extra-data set.
-func ValidateDAOHeaderExtraData(config *ChainConfig, header *types.Header) error {
+func ValidateDAOHeaderExtraData(config *params.ChainConfig, header *types.Header) error {
 	// Short circuit validation if the node doesn't care about the DAO fork
 	if config.DAOForkBlock == nil {
 		return nil