Update release notes for RC2
Update release notes for RC2

GabrielNicolasAvellaneda/riak,laurenrother/riak,xuejianhai/riak,planobe/riak,yangchengjian/riak,glickbot/riak,authbox-lib/riak,DavidAlphaFox/riak,elkingtonmcb/riak,planobe/riak,biddyweb/riak,amyvmiwei/riak,basho/riak