There's no reason for guides to reference old behaviors. They should
be current as of the versions of Rails that they ship with, and including
older information just clutters thing.

I discussed this change with @fxn and he agrees.

We have three or four different introduction sentences to the guides.
After this commit, we use the same one everywhere.

Talked with @fxn about this. Bullet points should have periods at the ends.

This reverts commit f5b9ed4f.

REASON: Translation work can not be done in the docrails repository

Change the default test locations to avoid confusion around the common
testing terms "unit" and "functional".
Add new rake tasks for the new locations, while maintaining backwards
compatibility with the old rake tasks.

New testing locations are as follows:

    app/models -> test/models (was test/units)
    app/helpers -> test/helpers (was test/units/helpers)
    app/controllers -> test/controllers (was test/functional)
    app/mailers -> test/mailers (was test/functional)

In Textile `*` would convert to `<strong>`, but in Markdown we have to
use `**` instead.

 explains how to add/override engine classes in the main rails app via
1) Class#class_eval
2) ActiveSupport::Concern

* comments.build will not actually persist the comment

update engines guide to show how to have an engine's ApplicationController inherit from the main application's ApplicationController

https://github.com/lifo/docrails/commit/bb23d6fb005edaf25f5b294f9215429fb44b3f3d