add Redis MSET support

Hello @x-ma, @don-neufeld, 

Please review the following commits I made in branch 'jamie-mset'.

b8efb84caf64871b630668a5af08c4d8363042d7 (2013-07-12 15:04:32 -0700)
add Redis MSET support


R=@x-ma
R=@don-neufeld