Fix Etag generation from source manifests
Fix Etag generation from source manifests

If source was uploaded by multipart, manifest's content-md5 is not
binary but 2-tuple.

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