Make RedisConnection.prototype.mget call underlying client with most performant argument pattern

Hello @majelbstoat, @x-ma, 

Please review the following commits I made in branch 'don-mget-order'.

ea1202945838b9f00f6c94ab4d22c8f6c0d83d12 (2013-07-30 18:53:12 -0700)
Make RedisConnection.prototype.mget call underlying client with most performant argument pattern


R=@majelbstoat
R=@x-ma