Modified Blog.cs CurrentPost() to check for a "key" query string parameter. When set to the ID of a post (GUID), allows an unauthenticated user to view the unpublished post.

i.e. http://server/post/test-1?key=a5e4d75a-6629-4942-aba3-8ed020d933f4
Merge pull request #154 from sam-ward/master

Modified Blog.cs CurrentPost() to check for a "key" query string parameter.