[conformal/btcd] cc9aad: Don't use headers first when checkpoints disabled.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: cc9aadf0415d726bc4d2d76e864416681344dec9
      
https://github.com/conformal/btcd/commit/cc9aadf0415d726bc4d2d76e864416681344dec9
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-12-20 (Fri, 20 Dec 2013)

  Changed paths:
    M blockmanager.go

  Log Message:
  -----------
  Don't use headers first when checkpoints disabled.

Headers first relies on having valid checkpoints, so if checkpoints are
disabled, it needs to be disabled as well.