[conformal/btcd] a26143: Use chan struct{} for throttling related chans.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: a261436e1b18ed537294dffeec1190097897f304
      
https://github.com/conformal/btcd/commit/a261436e1b18ed537294dffeec1190097897f304
  Author: Dave Collins <da...@conformal.com>
  Date:   2014-07-10 (Thu, 10 Jul 2014)

  Changed paths:
    M peer.go

  Log Message:
  -----------
  Use chan struct{} for throttling related chans.

The done and wait channels used to throttle outgoing data are being used
as semaphores.  As mentioned in the previous commit, it's more efficient
to use a 0-byte type and allow compiler optimizations for the specific use
case.