Remove old asset tags API from docs

This reverts commit e9d2ad39.

Closes #8460

Conflicts:
	activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
	activerecord/test/cases/dirty_test.rb

Add a test case to ensure that fractional second updates are detected.

Revert locale

action_on_unpermitted_parameters is present

This reverts commit 43e14f8f, reversing
changes made to bb17a0f0.

Conflicts:
	railties/lib/rails/generators/rails/app/templates/config/application.rb
	railties/lib/rails/generators/rails/app/templates/config/initializers/locale.rb

Reason: setting the Time.zone in an after_initialize block can become a
problem for people upgrading, since it's not going to be available when
config/initializers run, and people might be relying on it.

An example that I noticed was with the Chronic gem, for date/time parsing.
It requires us to configure the time class to be Time.zone, and doing
that in an initializer no longer worked with these changes, so reverting
is the safer path for now.

This reverts commit 39374aa9.

This reverts commit 46902908.

This was a suggestion of @carlosantoniodasilva, thanks!

Remove unnecessary require

`require 'rubygems'` is already required in Ruby 1.9 or later.

The sample application with the Getting Started Guide was very out of
date. I've re-done it on edge (as of 51b9def5) so it should
be good to go with Rails 4. It's also in synch with what the guide
actually says.

Stuff didn't work because of strong_parameters. Now the right calls are
in place.

We changed the error style, so they're all wrong. Now they're right.
😄

[ci skip]

[ci skip]

Adding Back Rails::Engine::Railties#engines

Conflicts:
	railties/CHANGELOG.md

Now we're almost ready to remove this: https://github.com/rails/rails/blob/5294ad8/activesupport/lib/active_support/test_case.rb#L29

The [following pull request](https://github.com/rails/rails/pull/8916) fixed
the block being passed to the appropriate helper method. However, the content
being passed into the block is generating repeated markup on the page due to
some weird ERb evaluation.

This commit tries to capture the block's generated output so the page isn't
flooded with markup.

[Rafael França + José Mota]

Closes #8936

Fix asset_path in mounted engine