CsvOutputFormatter only works for IEnumerable objects

[twsouthwick]

Looks like there is a check for if a result is IEnumerable while determining if the formatter applies. Is there a reason to require this? Can it just output an item in a single list?

[preeder]

This might be related to my pull request, which allows non-IEnumerable<T> results to still produce a header row. See https://github.com/WebApiContrib/WebAPIContrib.Core/pull/204