[conformal/btcwire] a7e3ee: Optimize writeTxOut.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcwire
  Commit: a7e3ee6aebc928fb5baa6595fb2f7ab797552a15
      
https://github.com/conformal/btcwire/commit/a7e3ee6aebc928fb5baa6595fb2f7ab797552a15
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-11-06 (Wed, 06 Nov 2013)

  Changed paths:
    M msgtx.go

  Log Message:
  -----------
  Optimize writeTxOut.

Before: BenchmarkWriteTxOut       500000              4050 ns/op
After:  BenchmarkWriteTxOut     10000000               248 ns/op

This is part ef the ongoing effort to optimize serialization as noted in
conformal/btcd#27.