Change error codes to strings so xml error documents will be properly generated.
Change error codes to strings so xml error documents will be properly generated.

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