Prevent Numeric#to_s from allocating an array

Bump required Ruby version to 2.1.0

[This article](http://weblog.rubyonrails.org/2014/8/20/Rails-4-2-beta1/#maintenance-consequences-and-rails-5-0) states that:

> Rails 5.0 is in most likelihood going to target Ruby 2.2.

Before the exact minimum version is fully decided, @arthurnn [suggests](https://github.com/rails/rails/pull/17830#issuecomment-64940383)
that **at least** version 2.1.0 **must** be required by the `gemspec` files.

Remove a reference to Ruby 1.9 in Guides

[ci skip]

Now that Rails requires Ruby >= 2.0 there is no need to document
Ruby 1.9.

[ci skip] fix class name

fixed indent of end in jdom.rb

Refactor `add_column_options!`, to move the quoting of default value for :uuid in `quote_value`.

delayed_job_active_record doesn't allow Rails 5 yet

We will support only Ruby >= 2.1.

But right now we don't accept pull requests with syntax changes to drop
support to Ruby 1.9.

4.2 release notes pass [skip ci]

Adds preloaded_records method to NullPreloader - fixes #16070

This fixes a regression where preloading association throws an
exception if one of the associations in the preloading hash doesn't
exist for one record.

Fixes #16070

Fixed a bug where AR::RecordNotSaved loses the given error message

Remove ecosystem link from guides

Refactor `SchemaCreation#visit_AddColumn`

Change originated from https://github.com/rails/rails/pull/17739#issuecomment-64829088

/cc @metaskills

Since 3e30c5d4, it started ignoring the given error message. This commit
changes the behavior of AR::RecordNotSaved#initialize so that it no
longer loses the given error message.

Correct test description for large integer test

This reverts commit 2a4e14db.

Update cookies.rb
Conflicts:
	actionpack/lib/action_dispatch/middleware/cookies.rb

[ci skip] Remove outdate note of :dependent in guide

Clarification follow-up to e2cce6cd [ci skip]

[skip ci]