[btcsuite/btcd] 5b14e1: mining: Add tests for prio queue. (#666)

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcd
  Commit: 5b14e157eabb9a00cee046f4e3467351eaf499d5
      
https://github.com/btcsuite/btcd/commit/5b14e157eabb9a00cee046f4e3467351eaf499d5
  Author: Dave Collins <d...@davec.name>
  Date:   2016-04-13 (Wed, 13 Apr 2016)

  Changed paths:
    A mining_test.go

  Log Message:
  -----------
  mining: Add tests for prio queue. (#666)

This adds a test to ensure the priority queue works properly both for
sorting by fee per KB and priorities.

Thanks to @ceejep for the original test code and idea which was
subsequently modified and cleaned up a bit to the code here.