== New: directories can have an index 'page'

I've decided that sometimes I really want a directory to have an
index page, not just a list of the contents. So now I can, with the
unimaginatively named 'index' view. It's mostly template based; the
normal template uses _inject::index_ to display an ((__index)) file.
However, the view has several special properties:

* unlike other directory views, it is not inherited by subdirectories.
* it is only listed as an available view in the page tools area if
  there is a file called ((__index)) in the directory.
* if ((__index)) is a redirection, the index view will just generate
  a redirect to the target.

(Thus, the index view could be used to replace the _wikiroot_
[[configuration directive ../ConfigurationFile]].)

The index view is valid on directories even without a ((__index))
page in the directory. Right now the template just displays a normal
directory listing in that case.