[btcsuite/btcd] 3d6afc: Move non-mempool specific functions to new file.

[David Hill]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcd
  Commit: 3d6afcffe7b758fcb7f65e1ef593c9cbca50f7ab
      
https://github.com/btcsuite/btcd/commit/3d6afcffe7b758fcb7f65e1ef593c9cbca50f7ab
  Author: David Hill <dh...@mindcry.org>
  Date:   2015-10-27 (Tue, 27 Oct 2015)

  Changed paths:
    M mempool.go
    A policy.go
    A policy_test.go

  Log Message:
  -----------
  Move non-mempool specific functions to new file.

No functional change. Add tests.