Add 21 known issue for Riak 1.2.0
Add 21 known issue for Riak 1.2.0

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