Many tests were using `render file:`, but were only testing the
behaviour of `render template:` (file: just allows more paths/ is less
secure then template:).
The reason for so many `render file:` is probably that they were the old
default.
This commit replaces `render file:` with `render template:` anywhere the
test wasn't specifically interested in using `render file:`.
This will silence deprecation warnings.
Most of the test can be changed from `render :text` to render `:plain`
or `render :body` right away. However, there are some tests that needed
to be fixed by hand as they actually assert the default Content-Type
returned from `render :body`.
The iteration object is available as the local variable
"template_name_iteration" when rendering partials with collections.
It gives access to the +size+ of the collection beeing iterated over,
the current +index+ and two convinicence methods +first?+ and +last?+
"template_name_counter" variable is kept but is deprecated.
[Joel Junström + Lucas Uyezu]
