Verify Content Types
Verify Content Types

- Added checks to verify that a RiakObject.ContentType is set using a properly formatted MIME Content Type.
- Parsing conforms only to the loosest rules - it checks to ensure that ContentType contains a "/" otherwise it throws a formatting error directing the user to http://en.wikipedia.org/wiki/MIME#Content-Type
- Fixes #8


Former-commit-id: c046148d940431c76816b3f902ec3fac9e00b9b9
rob-somerville/riak-dotnet-client,basho/riak-dotnet-client,basho/riak-dotnet-client,rob-somerville/riak-dotnet-client