Add missing param tags.
Add missing XML comments on NancyOwinHost.RequestEnvironmentKey
Add failing test to check that nancy appends Set-Cookie response header
Fix assertion to check correct cookie value
Append Set-Cookie values in Set-Cookie owin response header, if it already exists.
Merge pull request #1229 from damianh/Issue1228

Fixes Issue1228 - Set-Cookie values should be appended to owin response header