Before this commit, returning `false` in an ActiveModel `before_` callback
such as `before_create` would halt the callback chain.

After this commit, the behavior is deprecated: will still work until
the next release of Rails but will also display a deprecation warning.

The preferred way to halt a callback chain is to explicitly `throw(:abort)`.

Before this commit, returning `false` in an ActiveModel validation
callback such as `before_validation` would halt the callback chain.

After this commit, the behavior is deprecated: will still work until
the next release of Rails but will also display a deprecation warning.

The preferred way to halt a callback chain is to explicitly `throw(:abort)`.

After this commit, returning `false` in a callback will display a deprecation
warning to make developers aware of the fact that they need to explicitly
`throw(:abort)` if their intention is to halt a callback chain.

This commit also patches two internal uses of AS::Callbacks (inside
ActiveRecord and ActionDispatch) which sometimes return `false` but whose
returned value is not meaningful for the purpose of execution.

In both cases, the returned value is set to `true`, which does not affect the
execution of the callbacks but prevents unrequested deprecation warnings from
showing up.

This commit changes arguments and default value of CallbackChain's :terminator
option.

After this commit, Chains of callbacks defined **without** an explicit
`:terminator` option will be halted as soon as a `before_` callback throws
`:abort`.

Chains of callbacks defined **with** a `:terminator` option will maintain their
existing behavior of halting as soon as a `before_` callback matches the
terminator's expectation. For instance, ActiveModel's callbacks will still
halt the chain when a `before_` callback returns `false`.

This commit modifies the code (but not the purpose) of a test that checks that

> initializers are executed after application configuration initializers

Currently the test hard-codes the *exact* initializers that are expected to
occur before a custom one. This can cause the test to fail even if the
expectation still passes.

This commit loosens the test by simply checking that, in the array of
initializers, the custom initializers (called `dummy_initializer` in the
example) is executed after the last occurrence of `load_config_initializers`.

Refactoring of add_constraints in AssociationScope

Fix TaggedLogging to allow loggers to be instantiated multiple times without having to share the stack of tags

`MissingSourceFile` was just an alias to `LoadError` and was not
being raised inside the framework.

replace use of MissingSourceFile with LoadError

Conflicts:
	activesupport/test/core_ext/load_error_test.rb

Add missing nodoc's
Change `assoc_klass` argument name to `association_klass`
Change `prev_reflection` argument name to `previous_reflection`
Change `prev` to `previous_reflection` in `#get_chain`
Switch use of `refl` and `reflection` in `#get_chain` so main parameter
is not abbreviated.
Add missing space in `#add_constraints`

This moves the `#type_caster` from the `aliased_table_for` and into the
initialize of the `alias_tracker`.

`yield` instead of relying on checking if the reflection is equal to the
`chain_head`.

Instead of initializing an empty connection use the base table name
instead. Split up and refactor `#create` to be 2 methods `#create` and
`#create_with_joins`. Removes the need to update the count by 1 on
initialzing a JoinDependency.

This moves `alias_candidate` out of the `ReflectionProxy` and into the
`AbstractReflection` so it is shared by all reflections. Change
`alias_name` to a method and and remove assignment in `#get_chain`.

After the refactorings we're only using the connection and not the alias
tracker anymore. This builds on commit 18019.

Reuse the already available `@connection` to reduce the surface area of
the alias tracker's API. We can then remove the `attr_reader` because
the connection is already available.

This makes the `#alias_name` more functional.

Move `RuntimeReflection` and `PolymorphicReflect` into Reflection. This
allows the methods to inherit from `ThroughReflection` and DRY up the
methods by removing duplicates.

The linked list lets us use a loop in `#add_constraints` and completely
remove the need for indexing the iteration becasue we have access to the
next item in the chain.

By concatnating the `ReflectionProxy` with the `chain` we remove
the need for `#construct_tables` because the `chain` is now in the
correct order (order of the chain DOES matter).

Putting the `#alias_name` into ReflectionProxy means we don't have to
cache the `#alias_name` globally anymore - it's not cached per query.

`is_first_chain`, `items` and `klass` are no longer beneficial and can
be called directly instead of via their assignments - because they are
each only used once.

Move method structure into reflection classes for accessibly on each
reflection rather than by traversing the chain.

The `RuntimeReflection` class allows the reflection to be accessed at
runtime - then we always know which reflection we are accessing in the
chain. The `#get_chain` method then allows us to recursively access the
chain through the `RuntimeReflection`.

`#constraints` builds a flattened version of `scope_chain` to
allow it to be accessible without requiring an index when iterating
over the `scope_chain`

It already treats the message

Refactor `visit_ChangeColumnDefinition`

fix for messages in invalid encoding from db-drivers

Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
	activerecord/test/cases/connection_adapters/abstract_adapter_test.rb

`visit_ChangeColumnDefinition` is the same "CHANGE column_name " + `visit_ColumnDefinition(o)`.

In most cases, `create_table_definition` called by table_name (the first
argument) only.

Clear query cache on rollback

Add setting of FK for throgh associations while building

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/associations/has_many_through_associations_test.rb

Ensure append_info_to_payload is called even if an exception is raised.

Conflicts:
	actionpack/CHANGELOG.md

Make possible to use blocks with short version of render partial

Conflicts:
	actionview/CHANGELOG.md

Generate a hidden_tag when using a file_field

They are already present on Ruby 2.2

Improve a dump of the primary key support.

Conflicts:
	activerecord/CHANGELOG.md