message: Porting CHECKLOCKTIMEVERIFY
  Backported commit:
  commit
  Author: Peter Todd
  Date:   Mon Sep 29 01:00:01 2014 -0400
  Make CScriptNum() take nMaxNumSize as an argument
  While the existing numeric opcodes are all limited to 4-byte bignum
  arguments, new opcodes will need different limits.
diff: @@ -28,10 +28,10 @@ static const CBigNum bnZero(0);
  static const CBigNum bnOne(1);
  static const CBigNum bnFalse(0);
  static const CBigNum bnTrue(1);
  -static const size_t nMaxNumSize = 4;
  +static const size_t nDefaultMaxNumSize = 4;
  -CBigNum CastToBigNum(const valtype& vch)
  +CBigNum CastToBigNum(const valtype& vch, const size_t nMaxNumSize = nDefaultMaxNumSize)
  {
  if (vch.size() > nMaxNumSize)
  throw runtime_error("CastToBigNum() : overflow");
  