[conformal/btcscript] 4f4afe: Use the new btcec Signature.Serialize API.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcscript
  Commit: 4f4afedf39df65eceb4d7ca2b9b2eba4042cb49e
      
https://github.com/conformal/btcscript/commit/4f4afedf39df65eceb4d7ca2b9b2eba4042cb49e
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-12-23 (Mon, 23 Dec 2013)

  Changed paths:
    M script.go

  Log Message:
  -----------
  Use the new btcec Signature.Serialize API.

This commit modifies the code to use the new btcec Signature.Serialize API
instead of the internal sigDER which has now been removed.  This closes #3.

ok @owainga