Add a getvalue method to the base Payload class.  Also put a check in endpoint to make sure we have a Payload object before we call it's getvalue method.  Some of the awscli tests do some funny mocking that forces a raw string into the payload.
Check to make sure the operation's input attribute is not None before looking for a shape_name in it.
Remove typecheck for payload params

Require that if a payload object is set, it has to be
of type ``Payload``.  Updated the cli test that was not
obeying this contract.
Adding a test for iam get-group response parsing.  Related to https://github.com/boto/botocore/issues/62.
Merge branch 'develop' of github.com:boto/botocore into develop
Bumping version to 0.13.0
Merge branch 'release-0.13.0' into develop

* release-0.13.0:
  Bumping version to 0.13.0
Update dynamodb docs
Update opsworks docs
Update autoscaling docs
Update elasticbeanstalk docs
Update sqs docs
Update elb documentation
Update datepipeline docs
Update elastictranscoder service

* Doc updates
* MaxFrameRate
* Watermarks
Update sts model

* docs
* DecodeAuthorizationMessage added
Update cloudsearch docs
Remove xmlnamespace attr in emr model
Add in xmlnamespace in extra file
Update sns model

* Doc updates
* Switch to signature version 4