* It is not possible to always pre-determine the layout before going to ActionView.
This was *already* broken for render :partial => @object, :layout => true. This is
now handled by overriding render_to_body in layouts.rb and manually injecting the
partial's response. This needs to be done in ActionController since ActionController
knows enough to get _layout_for_option. There is probably a better abstraction here.
* As a result, all partial rendering can correctly restrict their layouts to the mime
type of the rendered partial. This could have previously caused a bug in some edge cases.
* If other layout-like options are added, they might need to add special code for the
case of render :partial. We should try to think of an alternate solution, if possible,
but this works for the cases we know of now.
* TODO: Review ActionController calling render_template for certain partials.
Might we be able to save logic by always delegating to AV's render_partial?
* _render_single_template, which renders a template without layout
* _render_partial_unknown_type, which renders a partial of unknown type
(the entry method for most partial rendering; supports strings, objects, and collections)
* _render_partial_object, which renders a partial for a single object.
* extracted _render_partial_path so it can be used to render the spacer without going
through the public render :partial
* rename _render_partial to _render_partial_unknown_type to reflect that for this call,
we don't know the type.
* Merge _render_partial_with_block and _render_partial_with_layout to _render_partial
* TODO: Check to see if any more logic can be shared
* TODO: See about streamlining block path so we can get rid of @_proc_for_layout
* Remove @exempt_from_layout as it is no longer needed
* remove no longer used _array_like_objects
* _render_content_with_layout renamed to _render_content since layout it optional
* remove check for optional layout before _render_content
* convert_content_type! is handled by assign_default_content_type_and_charset!
* set_content_length! should be handled by the endpoint server. Otherwise
each middleware that modifies the body has to do the expensive work of
recalculating content_length.
* convert_language! appears to be legacy. There are no tests for this
* convert_cookies! should be handled by the new HeaderHash in Rack
* Use an integer for .status's internal representation to avoid needing to
do String manipulation just to find out the status
