fixed RedundantCacheGroup to use promises properly

Hello @x-ma,

Please review the following commits I made in branch 'artem-fix-promises'.

960be11d2cf726b5addcb3c00d5e44ee8ae9bc32 (2013-08-06 15:41:03 -0700)
fixed RedundantCacheGroup to use promises properly


R=@x-ma