AS::Callbacks: deprecate monkey patch of object callbacks

Fix eagerly loading associations without primary keys

Fix Changelog example in Action Mailer [ci skip]

Update Active Record CHANGELOG for #7419 [ci skip]

Ensure valid migration filename on generating migration

move validation to AR

Fixed around callback with lambda example

This is a follow up to issue #7535

I have also chosen a variable name that matches the
parameter in the definition of load_missing_constant.

Those who say source code should be without comments lie.

Basically, const_missing had a loop to try parent namespaces
if the constant lookup failed, but at the same time delegated
to load_missing_constant which in turn also walks up parent
namespaces calling const_missing by hand. In the case of missing
constants this results in repeated work in some funky nested way.

Allow delivery method options to be set per mail instance

This will solve the issue that abort the connection transaction when we
skip the tests.

AR supporting new JSON data type on PostgreSQL >= 9.2

This implements the support to encode/decode JSON
data to/from database and creating columns of type
JSON using a native type [1] supported by PostgreSQL
from version 9.2.

[1] http://www.postgresql.org/docs/9.2/static/datatype-json.html

correct handling of changes in AR::Store, combine multiple store_accessors

Fix pluck when columns/tables are reserved words.

Use the 'mysql' binary for 'rake db:structure:load'

This will trim down the API and avoid some error that can be made
changing the cache object.

The previous implementation had the strange requirement that db/structure.sql contain only CREATE TABLE sql statements, one per table, separated by double newlines. SQLite3 and PostgreSQL database tasks, on the other hand, simply spawn 'sqlite3' and 'psql' binaries to load the file directly. The new implementation follows this and attempts to respect all current MySQL configuration settings.

We should not require all the core extensions inside the frameworks.
The logger is already defined in the Action View framework.

Fix for time type columns with invalid time value

Modularize postgresql adapter

The string_to_dummy_time method was blindly parsing the dummy time string
with Date._parse which returns a hash for the date part regardless
of whether the time part is an invalid time string.

Fix a typo in AD

Add an optional block to HashWithIndifferentAccess#update and #merge

When a block is passed into the method, it will be invoked for each
duplicated key, with the key in question and the two values as
arguments. The value for the duplicated key in the receiver will
be set to the return value of the block.

This behaviour matches Ruby's long-standing implementation of
Hash#update and is intended to provide a more consistent interface.

HashWithIndifferentAccess#merge is also affected by the change, as it
uses #update internally.

Refactor `Mime::Type`

`parse` method performance improvements - ~27-33%:

    accept = "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword,  , pronto/1.00.00, sslvpn/1.00.00.00, */*"

    Benchmark.measure{ 1_000_0.times { Mime::Type.parse(accept) }}

    old: 1.430000   0.000000   1.430000 (  1.440977)
    new: 0.920000   0.000000   0.920000 (  0.921813)