Handle failure of object deletion in riak_moss_wm_key.
Handle failure of object deletion in riak_moss_wm_key.

GabrielNicolasAvellaneda/riak_cs,basho/riak_cs,sdebnath/riak_cs,basho/riak_cs_report,dragonfax/riak_cs,basho/riak_cs_lfs,basho/riak_cs,sdebnath/riak_cs,GabrielNicolasAvellaneda/riak_cs,yangchengjian/riak_cs,sdebnath/riak_cs,laurenrother/riak_cs,GabrielNicolasAvellaneda/riak_cs,dragonfax/riak_cs,GabrielNicolasAvellaneda/riak_cs,basho/riak_cs,yangchengjian/riak_cs,laurenrother/riak_cs,yangchengjian/riak_cs,laurenrother/riak_cs,laurenrother/riak_cs,sdebnath/riak_cs,yangchengjian/riak_cs,basho/riak_cs,dragonfax/riak_cs,dragonfax/riak_cs