Simplified the S3 redirects plugin.

There is no need to parse the 'Location' header before constructing
an Endpoint object.
Added Service#default_client_class.

This helper returns the actual versioned Seahorse client.
Previously you could only get the default api version.
Improved the documentation around global version locks.
Removed the OperationNameResult wrappers from the APIs.

Recently these extra wrappers were added the APIs so they would
match the response XML.  This had the undesirable effect of nesting
response data an extra layer.

These wrappers have been removed and the XML parser now manages
removing the extra wrapper from the result.