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/vm/jit.go

@@ -319,7 +319,7 @@ func runProgram(program *Program, pcstart uint64, mem *Memory, stack *Stack, env
 		}()
 	}
 
-	homestead := env.RuleSet().IsHomestead(env.BlockNumber())
+	homestead := env.ChainConfig().IsHomestead(env.BlockNumber())
 	for pc < uint64(len(program.instructions)) {
 		instrCount++