JSON gem compatibility

Previously, calling `::JSON.{generate,dump}` sometimes causes
unexpected failures such as intridea/multi_json#86.

`::JSON.{generate,dump}` now bypasses the ActiveSupport JSON encoder
completely and yields the same result with or without ActiveSupport.
This means that it will **not** call `as_json` and will ignore any
options that the JSON gem does not natively understand. To invoke
ActiveSupport's JSON encoder instead, use `obj.to_json(options)` or
`ActiveSupport::JSON.encode(obj, options)`.

Revert "Used Yield instead of block.call" -- this causes all of atom_feed_helper_test.rb to fail with "SystemStackError: stack level too deep".

This reverts commit d3a1ce1c.

Fix that eager loading of polymorphic associations did not work with association empty?/any? predicates any more (there is still a problem when select is applied to a relation, or if you try association#exists? -- but its easier to work around)

Addendum to #12891

Also dup `column_types` in AR::Result `initialize_copy`

* Fix incorrectly named tests
* Restore Object#to_param behavior
* Ensure param is derived from a squished and truncated string

avoiding next statements

Used Yield instead of block.call

Add AR::Base.to_param for convenient "pretty" URLs derived from a model's attribute or method

class methods moved to already defined class<<self block

#presence used

Clean up `require ‘active_support/deprecation’` and remove circular require

Move `SchemaCreation` to its own file instead of `AbstractAdapter`.

Ruby's new Hash syntax applied in actionmailer

Refer to Rails.env from AR only when Rails is defined

Updated guides link for 3.2.x to latest stable version 3.2.15 [ci skip]

Use rescue with a splat rather and catching all exceptions and manually filtering in Kernel#suppress

Make it clear that require 'active_support' is required [ci-skip]

Add No Touching

Fix syntax error in atom_feed example [ci skip]

Builder's #tag! takes either String or Symbol as the first parameter

As of Rails 4.0 `remove_column` is no longer an alias for `remove_columns`.
The type is actually valid and used when issuing a rollback (new `change` method).

This reverts commit 9c9d4948.

[ci skip] Fix curl response output and use strong parameters in update action