[conformal/btcchain] 79beb2: Export CoinbaseMaturity as a const.

[Josh Rickmar]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcchain
  Commit: 79beb22aef5e72bebd924bc3c64dc2d64c8c2ff9
      
https://github.com/conformal/btcchain/commit/79beb22aef5e72bebd924bc3c64dc2d64c8c2ff9
  Author: Josh Rickmar <jr...@conformal.com>
  Date:   2014-04-14 (Mon, 14 Apr 2014)

  Changed paths:
    M validate.go

  Log Message:
  -----------
  Export CoinbaseMaturity as a const.

The unexported variable is still kept so that tests may modify it.

ok @davecgh