Commented Issue: Setting route value in route conventions instead of adding [756]

This fix is try to workaround tracing issue: http://aspnetwebstack.codeplex.com/workitem/755
As route convention will be run twice, it will cause duplicate keys are inserted to route values collection and result in duplicate key exception thrown.

The workaround is to set those values instead of adding. So even it's already there, it won't cause exception and the logic doesn't change.
Comments: Fixed: http://aspnetwebstack.codeplex.com/SourceControl/changeset/5d93e7c34915