Add `#travel` and `#travel_to` to `ActiveSupport::TestCase`

Add `ActiveSupport::Testing::TimeHelpers#travel` and `#travel_to`. These
methods change current time to the given time or time difference by
stubbing `Time.now` and `Date.today` to return the time or date after
the difference calculation, or the time or date that got passed into the
method respectively. These methods also accept a block, which will
return current time back to its original state at the end of the block.

Example for `#travel`:

    Time.now # => 2013-11-09 15:34:49 -05:00
    travel 1.day
    Time.now # => 2013-11-10 15:34:49 -05:00
    Date.today # => Sun, 10 Nov 2013

Example for `#travel_to`:

    Time.now # => 2013-11-09 15:34:49 -05:00
    travel_to Time.new(2004, 11, 24, 01, 04, 44)
    Time.now # => 2004-11-24 01:04:44 -05:00
    Date.today # => Wed, 24 Nov 2004

Both of these methods also accept a block, which will return the current
time back to its original state at the end of the block:

    Time.now # => 2013-11-09 15:34:49 -05:00

    travel 1.day do
      User.create.created_at # => Sun, 10 Nov 2013 15:34:49 EST -05:00
    end

    travel_to Time.new(2004, 11, 24, 01, 04, 44) do
      User.create.created_at # => Wed, 24 Nov 2004 01:04:44 EST -05:00
    end

    Time.now # => 2013-11-09 15:34:49 -05:00

This module is included in `ActiveSupport::TestCase` automatically.

Update caching guide with respect to :namespace

Cache::Store does not have a default value for :namespace. If it ever did, I can't find it in the git history.

Closes #12831

Improve readability of sentence in partial-renderer docs [ci skip]

This fixes a bug when merging relations of different classes.

```
Given:
  Post.joins(:author).merge(Author.order(name: :desc)).to_sql

Before:
 SELECT "posts".* FROM "posts"
   INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
   ORDER BY "posts"."name" DESC

After:
 SELECT "posts".* FROM "posts"
   INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
   ORDER BY "authors"."name" DESC
```

This reverts commit fbcd46b1.

This is not needed anymore. See 72809654

This reverts commit 22f80ae5.

See
https://github.com/rails/rails/commit/22f80ae57b26907f662b7fd50a7270a6381e527e#commitcomment-4640676

Conflicts:
	activerecord/CHANGELOG.md

This is a follow-up to 3053fee9.

> The `master` branch should use the `master` branch.

this resolves the following error when running `bundle install`

```
ArgumentError: wrong number of arguments (2 for 1)
    /Users/senny/Projects/rails/.bundle/bundler/gems/arel-454a25f18c95/lib/arel/crud.rb:5:in `compile_update'
```

The build is still broken with lots of:

```
ArgumentError: wrong number of arguments (2 for 1)
    /Users/senny/Projects/rails/.bundle/bundler/gems/arel-454a25f18c95/lib/arel/crud.rb:5:in `compile_update'
```

[ci skip] `apropriate` => `appropriate`, spaces added

Fixed typos in "shallow routes" and "routing concerns" in routing.md [ci skip]

`skiping` => `skipping` [ci skip]

Grammatical tense correction: "There exists two" => "There exist two".
Plurality correction: "can be reused inside others resources" => "can be reused inside other resources".

added test cases to find notes in a file with .builder extension

Do not count query for all_constraints and all_tab_cols tested with Oracle

Address test_merging_where_relations failure by adding order

This will help identify these tasks exists, since they are easier to
setup things for running all AR tests.

Fix travis failures.

Drop unused param `should_be_quoted` to `PostgreSQLColumn#array_to_string`

[ci skip]updated documentation: added sass and less extensions

Build fix for ruby 1.9.3 syntax

Checks to see if the record contains the foreign_key to set the inverse automatically

Conflicts:
	activerecord/CHANGELOG.md

Track initializer's loaded event per file