fix issue 411, /path/to/site/archetypes : is a directory error

https://github.com/spf13/hugo/issues411

   ERROR: 2014/08/15 read /path/to/site/archetypes: is a directory

occurs because creating new content with a content type results in kind = "". Since the original `pathsToCheck` automatically included kind variants, an empty kind would result in the `is a directory` error.

The resolution is to check to see if kind is empty and if it is, only check for `default.md` and 'default`, otherwise do the path checks with the kind included.