Pare down and simplify Active Job's rake tasks
Tighten up AJ::Arguments and its tests

* Disallow deserialization of non-primitive objects
* Broaden coverage; remove superfluous tests
simplify test_adapter
Merge pull request #16918 from kiuru/master

Singular credit_card controller name changed to plural [ci skip]
Merge pull request #16920 from seuros/aj

simplify test_adapter
handle <%== nil %> cases

This is much less common than string literal appends, so add a special
case method for it.  Maybe fixes bug reported by @jeremy on 97ef636191933f1d4abc92fc10871e6d1195285c
Add `test:jobs` task
Merge pull request #16922 from y-yagi/add_test_jobs_task

Add test jobs task
add implementation of respond_to? for ActiveSupport::Duration
Merge pull request #16574 from lsylvester/duration-respond_to

add implementation of respond_to? for ActiveSupport::Duration
As of Unicode 6.3, Mongolian Vowel Separator is not whitespace

Ruby 2.2 knows this, and no longer matches it with [[:space:]], so it's
not a good candidate for testing String#squish.
Don't autosave unchanged has_one through records
[ci skip] Fix typo `equals to` --> `equal to`
Merge pull request #16927 from akshay-vishnoi/fix-typo

[ci skip] Fix typo `equals to` --> `equal to`
[ci skip] Fix code snippet display in Action Mailer Basics guide.
Make explicit 4.1 is being maintained by a special situation

[ci skip]
Merge pull request #16914 from untidy-hair/fix_plugin_dummy_path_error

Use dynamic path for dummy app location in plugin's test_helper.rb
Merge pull request #16790 from cirosantilli/explain-erb-space-removal

Explain ERB space removal.

[ci skip]
Added Responders docs, made Web Console docs more consistent. [ci skip]
Backwards compat for activerecord-deprecated_finders

Maintain compatibility for:
* ActiveRecord::Base#find(:all)
* ActiveRecord::Base#find(:first)
* ActiveRecord::Base#find(:last)