[conformal/btcchain] 6165e9: Convert API to use new btcutil.Tx.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcchain
  Commit: 6165e9b95bf1fb7914dc9220c85b223117c9b5e3
      
https://github.com/conformal/btcchain/commit/6165e9b95bf1fb7914dc9220c85b223117c9b5e3
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-10-28 (Mon, 28 Oct 2013)

  Changed paths:
    M accept.go
    M checkpoints.go
    M internal_test.go
    M merkle.go
    M scriptval.go
    M txlookup.go
    M validate.go
    M validate_test.go

  Log Message:
  -----------
  Convert API to use new btcutil.Tx.

This is part of the ongoing transaction hash optimization effort noted in
conformal/btcd#25.