Removes OS specific directory separator

Handle `FrozenError` if it is available

Fix Illegal parameter data type bigint for operation 'get_lock' error

This pull request handles `FrozenError` introduced by Ruby 2.5.
Refer https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/61131

Since `FrozenError` is a subclass of `RuntimeError` minitest used by master
branch can handle it, though it would be better to handle `FrozenError`
explicitly if possible.

`FrozenError` does not exist in Ruby 2.4 or lower, `frozen_error_class`
handles which exception is expected to be raised.

This pull request is intended to be merged to master,
then backported to `5-1-stable` to address #31508

Follow up of #31289.

Follow up of #31177.

Like other query bang methods.

Remove verbose_query_logs from new_framework_defaults_5_2.rb

The `app:update` rake task will regenerate `development.rb` so that it
contains this option; that means we're currently adding it to existing
apps in two places, which is unnecessary and confusing.

Also:
 - Remove inaccurate comment about which stack frames are ignored
 - Clarify that the feature uses `caller_locations`, not `caller`
 - Remove unused return value in `extract_callstack`

Remove default ENGINE=InnoDB for Mysql2 adapter

Currently `count(:all)` with `distinct` doesn't work correctly because
SELECT list is always replaced to `*` or primary key in that case even
if having custom SELECT list.

And also, PostgreSQL has a limitation that ORDER BY expressions must
appear in select list for SELECT DISTINCT.

Therefore, we should not replace custom SELECT list when using
`count(:all)` with `distinct`.

Closes #31277.

Merge pull request #31483 from yhirano55/fix_validation_callbacks_on_multiple_context_in_active_model

Bugfix: validation callbacks on multiple context

I found a bug that validation callbacks don't fire on multiple context.
So I've fixed it.

Example:

```ruby
class Dog
  include ActiveModel::Validations
  include ActiveModel::Validations::Callbacks

  attr_accessor :history

  def initialize
    @history = []
  end

  before_validation :set_before_validation_on_a, on: :a
  before_validation :set_before_validation_on_b, on: :b
  after_validation :set_after_validation_on_a, on: :a
  after_validation :set_after_validation_on_b, on: :b

  def set_before_validation_on_a; history << "before_validation on a"; end
  def set_before_validation_on_b; history << "before_validation on b"; end
  def set_after_validation_on_a;  history << "after_validation on a" ; end
  def set_after_validation_on_b;  history << "after_validation on b" ; end
end
```

Before:

```
d = Dog.new
d.valid?([:a, :b])
d.history # []
```

After:

```
d = Dog.new
d.valid?([:a, :b])
d.history # ["before_validation on a", "before_validation on b", "after_validation on a", "after_validation on b"]
```

assert_nothing_raised not required here, we can assert directly for the actual result

Otherwise it will occur syntax error if primary key is a reserved word.

Arel doesn't support subselect generation for DELETE unlike UPDATE yet,
but we already have that generation in connection adapters. We can
simply use the subselect generated by that one.

Most RDBMS (except SQLite) requires subselect for UPDATE with OFFSET,
but Arel doesn't support executable subselect generation for MySQL's
UPDATE yet. We need to use the subselect generated by the connection
adapter for now, it works well.

Fixes #30148.

[ci skip] Added Object Relational Mapping wiki link

Undefine attribute methods of descendants when resetting column information

Specifying the `--dev` option is when want to change the codebase,
as it is not necessary to cache it.

Context: https://github.com/rails/rails/pull/31485#issuecomment-352452653

Raise an error only when `require_master_key` is specified

Update new_framework_defaults_5_2.rb.tt

Be consistent in comments when mentioning AES.

Add headless browser support in api docs [ci skip]

Add `skip_bootsnap` option

Clarify docs for delegate :allow_nil option

Don't include ellipsis in truncated digest output

To prevent errors from being raise in environments where credentials
is unnecessary.

Context: https://github.com/rails/rails/issues/31283#issuecomment-348801489

Fixes #31283

Looks like it is failed due to datetime rounding. Related #23521.

https://travis-ci.org/rails/rails/jobs/317734560#L1980-L1984

Previously table name qualified `*` is used in that case. If it is not
qualified with a table name, an ambiguous column name error will occur
when using JOINs.

Thanks to @Datasnuten for the suggestion.