Fix secure_password password_confirmation validations

Move model mutation to the methods that are called on the model.

add the missing middleware in command line guides rake about [ci skip]

assert_file already gives this functionality for free by passing
multiple contents.

Uses mysql2 0.3.13 or later.

content tag already knows which tags are boolean and the values that
should generate them when a truthy value is passed, so leave this logic
for it instead of duplicating when generating options tags.

Fixes #11454 . We should define the return type of select_all method clearly.

Showing welcome page in production can expose information, which should
not be visible on production if people don't override the default root
route.

This reverts commit b0caea29.

[Fixes #11512] improves cache size calculation in MemoryStore

Previously, the cache size of `ActiveSupport::Cache::MemoryStore` was calculated
as the sum of the size of its entries, ignoring the size of keys and any data
structure overhead. This could lead to the calculated cache size sometimes being
10-100x smaller than the memory used, e.g., in the case of small values.

The size of a key/entry pair is now calculated via `#cached_size`:

    def cached_size(key, entry)
      key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
    end

The value of `PER_ENTRY_OVERHEAD` is 240 bytes based on an [empirical
estimation](https://gist.github.com/ssimeonov/6047200) for 64-bit MRI on
1.9.3 and 2.0.

Fixes GH#11512 https://github.com/rails/rails/issues/11512

Rebase and make fixes to #6763 "Specified column type for quote_value" 

syntax fix f.select doc

Removed random dot in ActionController docs [ci skip]

Remove duplication in include test

metal is no longer mentioned on rack guide