Two bugfixes, one for httplib.BadStatusLine and one for Unicode in Riak Search

There are two commits here to fix two different problems (it seemed awkward to make them independent pull requests). 

One makes the client retry upon receiving httplib.BadStatusLine, which fixes issue #209.

The other commit fixes some UnicodeDecodeErrors that occured because the Riak Search interface assumed everything was a bytestring. It was impossible to send non-ASCII data to Riak Search. Now, instead, it encodes all XML and query strings as UTF-8. These UTF-8 strings naturally turn into the appropriate Unicode when returned in JSON results.