[conformal/btcd] 629168: Perform display handler check before issues RPC.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: 629168b7ae71972a771cfbb7bb6b9ef7d98d4894
      
https://github.com/conformal/btcd/commit/629168b7ae71972a771cfbb7bb6b9ef7d98d4894
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-10-21 (Mon, 21 Oct 2013)

  Changed paths:
    M util/btcctl/btcctl.go

  Log Message:
  -----------
  Perform display handler check before issues RPC.

This commit modifies the command handler in btcctl to check the existence
of a display handler before issues an RPC command.  This prevents a round
trip to the server if there is no display handler.

Also, fix a couple of comments while here.