HashWithIndifferentAccess#select working as intended

Before this commit, #reject returned a HashWithIndifferentAccess,
whereas #select returned a Hash. Now #select also returns a
HashWithIndifferentAccess.
Refactored ActiveRecord `first` method to get rid of duplication.
rename method `find_first_records` to `find_first_with_limit`
Merge pull request #10898 from dmitry/find_first_refactor_duplication

Refactored ActiveRecord `first` method to get rid of duplication.
Merge pull request #10740 from mrsimo/hash-with-indifferent-access-select

HashWithIndifferentAccess#select working as intended
Add CHANGELOG entry for #10740

[ci skip]
valid_app_const? -> valid_const?
Changing const_regexp to check for constant name.

We need to return Regexp.escape(camel_cased_word)
if the split is blank.
Merge pull request #10946 from arunagw/build_fix_for_object_const_get_nil

We need to check exception name to be nil
Merge pull request #10950 from appscape-forks/fix-wrong-method-name

Fix wrong method name
Update the HTML boolean attributes per the HTML 5.1 spec

- Add attributes `allowfullscreen`, `default`, `inert`, `sortable`,
`truespeed`, `typemustmatch`.
- Fix attribute `seamless` (previously misspelled `seemless`).
- Use `assert_dom_equal` instead of `assert_equal` in test.
Fix AS changelog [ci skip]
fix typos
Merge pull request #10953 from acapilleri/fix_typos

fix typos
'json' gem is no more required under JRuby
cleanup, remove trailing whitespace from AR changelog
regression test + mysql2 adapter raises correct error if conn is closed.
Merge pull request #10925 from senny/10917_test_to_prevent_regression

regression test + mysql2 adapter raises correct error if conn is closed.
Merge pull request #10955 from arunagw/jruby_json_not_required

'json' gem is no more required under JRuby
fixture setup does not rely on `AR::Base.configurations`.

As you can also configure your database connection using `ENV["DATABASE_URL"]`,
the fixture setup can't reply on the `.configurations` Hash.

As the fixtures are only loaded when ActiveRecord is actually used
(`rails/test_help.rb`) it should be safe to drop the check for an existing configuration.