[btcsuite/btcwallet] d09c2a: Protect the relay fee field with a mutex.

[Josh Rickmar]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcwallet
  Commit: d09c2a84c196a504e36db280fa89d34a338efb18
      
https://github.com/btcsuite/btcwallet/commit/d09c2a84c196a504e36db280fa89d34a338efb18
  Author: Josh Rickmar <jr...@companyzero.com>
  Date:   2016-03-09 (Wed, 09 Mar 2016)

  Changed paths:
    M rpc/legacyrpc/methods.go
    M wallet/createtx.go
    M wallet/wallet.go

  Log Message:
  -----------
  Protect the relay fee field with a mutex.

This prevents races when setting a new relay fee through the legacy
RPC server (settxfee).

Fixes #379.