Fixes AR mysql2 adapter incorrectly casting boolean values

Using the mysql2 adapter, boolean values were sometimes being incorrectly cast
to 't' or 'f'. This changes the cast to match the mysql adapter behavior, ie 1 and 0.

Added generated unit test for generator generator.

Added generated unit test for generator generator and new test:generators rake task included in test:all rake task.

Do not re-save destroyed association on saving parent object

Closes #11450

Remove deprecated `attribute_missing`.

for attributes that are columns.

No need to add config for x_sendfile_header

As this middleware comes by default in a new
rails app

Added test to check omit for CheckPending when

Active Record is not included.

Rack::Sendfile is loaded by default now

This reverts commit 19ac034b.
And allows webservers to configure X-Sendfile-Type.

Closes #11440 thanks to [@MSch]

Conflicts:
	railties/lib/rails/application.rb

Remove extra decrement of transaction level

Blacklist->whitelist for reference scans in order!

See https://github.com/rails/rails/commit/da9b5d4a8435b744fcf278fffd6d7f1e36d4a4f2#commitcomment-3630064 for discussion.

Stop special-casing Arel::Nodes as exempt from reference scanning in
order. Instead, only scan order values that are strings for a table
reference.

`rollback_active_record_state!` tries to restore model state on `Exception`
by invoking `restore_transaction_record_state` it decrement deep level by `1`.

After restoring it ensure that states to be cleared
and level decremented by invoking `clear_transaction_record_state`,
which cause the bug: because state already reduced in `restore_transaction_record_state`.

Removed double derement of transaction level
and removed duplicated code which clear transaction state for top level.

Fix #11393. Fix default rendered format when calling render method without :content_type option.

Fix default rendered format problem when calling render method without :content_type option. Closes #11393.

railties Rakefile tweaks

Actionview api generation

memorized -> memoized typo fix [ci skip]

Reverts one line from 457b7ff9

CHANGELOG and LICENSE removed as suggested 

Reset @column_defaults when assigning locking_column.

Update YUI Compressor link; tweak UglifyJS

ActionController::Live documentation in the guides.

it's xml, not json

change docs for xml serializer to talk about xml