[ci skip] Mention the change in nil handling for serialized attributes
in "Upgrading from Rails 3.2 to Rails 4.0"
[ci skip] Clarify the "Serialized Attributes" section

Mention that the change in nil handling for serialized attributes
affects custom coders.
Allow password to contain spaces only.
lazily instantiate application subclasses

this means we can meaningfully override methods in the subclass
Fix DateTime comparison with DateTime::Infinity object

Fixes #16406
Test using turbolinks master

See
https://github.com/rails/turbolinks/commit/153f1b0f04c718442cfd73365a2778dfe1a1c5c7
Define id_was to get the previous value of the primary key

Currently when we call id_was and we have a custom primary key name
Active Record will return the current value of the primary key. This
make impossible to correctly do an update operation if you change the
id.

Fixes #16413
[ci skip] Updated create! documentation description and added +attributes+ for rdoc
Remove ActionController::RaiseActionExceptions.

The latest modification to the code was done in https://github.com/rails/rails/commit/5e3517ea. In Rails 3.2,
`ActionController#rescue_action` was deprecated and `rescue_action_without_handler` is no longer being used.
Merge pull request #16419 from tgxworld/remove_legacy_code

Remove ActionController::RaiseActionExceptions.
Merge pull request #16412 from yevhene/master

Fix in has_secure_password for passwords containing only spaces.
Fix typo [ci skip]
Tables existence check query is executed in large quantities

When Rails starts, tables existence check query is executed
number of models.
In case of mysql,

    SHOW TABLES LIKE 'table1';
    SHOW TABLES LIKE 'table2';
    SHOW TABLES LIKE 'table3';
    ...
    SHOW TABLES LIKE 'table999';

Add process to get the names of all tables by one query.
Fix spelling.
Merge pull request #16422 from tgxworld/fix_spelling

Closes #16422
change to empty? from blank?
Merge pull request #16421 from tsukasaoishi/prevant_manycall_showtables

Tables existence check query is executed in large quantities
use the uri parser so that newer version of Ruby work
remove dead file_watcher code
Merge pull request #16424 from gregors/remove_dead_code

remove dead file_watcher code