[conformal/btcd] daa531: Add support for debuglevel RPC command.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: daa5310e2f1e1051ad84b5078dcd2cf159f662f7
      
https://github.com/conformal/btcd/commit/daa5310e2f1e1051ad84b5078dcd2cf159f662f7
  Author: Dave Collins <da...@conformal.com>
  Date:   2013-11-22 (Fri, 22 Nov 2013)

  Changed paths:
    M config.go
    M rpcserver.go
    M util/btcctl/btcctl.go

  Log Message:
  -----------
  Add support for debuglevel RPC command.

Also include the supported subsystems in the error message if an invalid
subsystem is specified.

Closes #15.