Remove unnecessary `Hash#to_a` call

Inspired by https://github.com/rails/rails/commit/931ee4186b877856b212b0085cd7bd7f6a4aea67

```ruby

def stat(num)
  start = GC.stat(:total_allocated_object)
  num.times { yield }
  total_obj_count = GC.stat(:total_allocated_object) - start
  puts "#{total_obj_count / num} allocations per call"
end

h = { 'x' => 'y' }

stat(100) { h.     each { |pair| pair } }
stat(100) { h.to_a.each { |pair| pair } }

__END__
1 allocations per call
2 allocations per call
```
Rename `stack` to `queue`

Because it is used as a queue (FIFO), not as a stack (LIFO).

* http://en.wikipedia.org/wiki/Stack_(abstract_data_type)
* http://en.wikipedia.org/wiki/Queue_(data_structure)
Merge pull request #15252 from DNNX/formatter-refactoring-2

Remove unnecessary `Hash#to_a` call
Move `extract_precision` onto type objects
Merge pull request #15239 from croaky/dc-sg-move-extract-precision-to-types

Move `extract_precision` onto type objects
Push scale to type objects

Ideally types will be usable without having to specify a sql type
string, so we should keep the information related to parsing them on the
adapter or another object.
Merge pull request #15254 from DNNX/formatter-refactoring-3

Rename `stack` to `queue`
Merge pull request #15250 from sgrif/sg-push-scale-to-types

Push scale to type objects
Push precision to type objects
Removed not-used code
Merge pull request #15256 from sgrif/sg-push-precision-to-types

Push precision to type objects
Push limit to type objects

Columns and injected types no longer have any conditionals based on the
format of SQL type strings! Hooray!
Merge pull request #15259 from sgrif/sg-push-limit-to-types

Push limit to type objects
Don't recurse infinitely when calling non-existent method on super
fix test from 7537057888d2d63c3b6c2019d5828bc445fbd6c9
Merge pull request #15257 from jetthoughts/remove_redundant_code

Removed not used code
Fixed serialization for records with an attribute named `format`.

* * *

This bug can be triggered when serializing record R (the instance) of type C
(the class), provided that the following conditions are met:

1. The name of one or more columns/attributes on C/R matches an existing private
   method on C (e.g. those defined by `Kernel`, such as `format`).

2. The attribute methods have not yet been generated on C.

In this case, the matching private methods will be called by the serialization
code (with no arguments) and their return values will be serialized instead. If
the method requires one or more arguments, it will result in an `ArgumentError`.

This regression is introduced in d1316bb.

* * *

Attribute methods (e.g. `#name` and `#format`, assuming the class has columns
named `name` and `format` in its database table) are lazily defined. Instead of
defining them when a the class is defined (e.g. in the `inherited` hook on
`ActiveRecord::Base`), this operation is deferred until they are first accessed.

The reason behind this is that is defining those methods requires knowing what
columns are defined on the database table, which usually requires a round-trip
to the database. Deferring their definition until the last-possible moment helps
reducing unnessary work, especially in development mode where classes are
redefined and throw away between requests.

Typically, when an attribute is first accessed (e.g. `a_book.format`), it will
fire the `method_missing` hook on the class, which triggers the definition of
the attribute methods. This even works for methods like `format`, because
calling a private method with an explicit receiver will also trigger that hook.

Unfortunately, `read_attribute_for_serialization` is simply an alias to `send`,
which does not respect method visibility. As a result, when serializing a record
with those conflicting attributes, the `method_missing` is not fired, and as a
result the attribute methods are not defined one would expected.

Before d1316bb, this is negated by the fact that calling the `run_callbacks`
method will also trigger a call to `respond_to?`, which is another trigger point
for the class to define its attribute methods. Therefore, when Active Record
tries to run the `after_find` callbacks, it will also define all the attribute
methods thus masking the problem.

* * *

The proper fix for this problem is probably to restrict `read_attribute_for_serialization`
to call public methods only (i.e. alias `read_attribute_for_serialization` to
`public_send` instead of `send`). This however would be quite risky to change
in a patch release and would probably require a full deprecation cycle.

Another approach would be to override `read_attribute_for_serialization` inside
Active Record to force the definition of attribute methods:

   def read_attribute_for_serialization(attribute)
     self.class.define_attribute_methods
     send(attribute)
   end

Unfortunately, this is quite likely going to cause a performance degradation.

This patch therefore restores the behaviour from the 4-0-stable branch by
explicitly forcing the class to define its attribute methods in a similar spot
(when records are initialized). This should not cause any extra roundtrips to
the database because the `@columns` should already be cached on the class.

Fixes #15188.
Avoid slowing down AR object initialization

2d73f5a forces AR to enter the `define_attribute_methods` method whenever it
instantiate a record from the `init_with` entry point. This is a potential
performance hotspot, because `init_with` is called from all `find*` family
methods, and `define_attribute_methods` is slow because it tries to acquire
a lock on the mutex everytime it is entered.

By using [DCL](http://en.wikipedia.org/wiki/Double-checked_locking), we can
avoid grabbing the lock most of the time when the attribute methods are already
defined (the common case). This is made possible by the fact that reading an
instance variable is an atomic operation in Ruby.

Credit goes to Aaron Patterson for pointing me to DCL and filling me in on the
atomicity guarantees in Ruby.

[*Godfrey Chan*, *Aaron Patterson*]
use symbol keys for path_parameters
just return path parameters