Make actioncable ready for frozen strings

Use frozen string literal in actionmailer/

Fix a failued AR test when using OracleAdapter

[ Assain Jaleel & Kasper Timm Hansen ]

[ Assain Jaleel & Kasper Timm Hansen ]

So releasing 5.1 and 5.0 together won't require manual copy
and paste.

Basically revises the release flow to:

* Update the version in RAILS_VERSION + rake changelog:header
* Run rake all:verify (click around in the booted app)
* If that checks out, run rake release.

Sort enabled adapter extensions in schema dump

Use `TRUE` and `FALSE` boolean literals for MySQL

Use `ArgumentError` instead of own error class

Make `type_map` to private because it is only used in the connection adapter

Updates Rails upgrade guide on `ActionView::Helpers::RecordTagHelper`

Fix false positive test related to wrong app root path.

Match destroyed_by_association for has_one to has_many

Use frozen-string-literal in ActiveRecord

This reverts commit b6ad4052.

This is not something that the majority of Active Record should be
testing or care about. We should look at having fewer places rely on
these details, not make it easier to rely on them.

When a has_many association is destroyed by `dependent: destroy`,
destroyed_by_association is set to the reflection, and this can be
checked in callbacks.  This matches that behaviour for has_one
associations.

Without setting root config, `config.paths["config/secrets"]`
located in https://github.com/rails/rails/blob/84eb498f84ebc5d1be0b0db6f7bca9da3d679ca6/railties/lib/rails/application.rb#L390
always returned empty list.

Remove log directory in test postprocessing

Updates Rails upgrade guide for 4.2 to 5.0 regarding the removal of `ActionView::Helpers::RecordTagHelper`

The "log" is directory. So it is necessary to use `FileUtils.rm_rf`.

This fixes the following failures.
https://travis-ci.org/rails/rails/jobs/253990014

Add jQuery to test/ujs/vendor files for testing rails-ujs

Make `rails yarn:install` ignore dev dependencies

... so that we can run most, if not all, of rails-ujs
tests without necessarily requiring an internet connection.

`type_map` is an internal API and it is only used in the connection
adapter. And also, some type map initializer methods requires passed
`type_map`, but those instances already has `type_map` in itself.
So we don't need explicit passing `type_map` to the initializers.

Since #29699, abstract boolean serialization has been changed to use
`TRUE` and `FALSE` literals. MySQL also support the literals.
So we can use the abstract boolean serialization even for MySQL.

If the argument is invalid, I think that it is more intuitive to use
`ArgumentError` than its own error class.

Add Expiry & Purpose to Message Verifier

Add purpose and expiry to messages encrypted using Message Encryptor