Merge pull request #13104 from christophemaximin/fix_robots_txt_link

Fix URL to robots.txt documentation [ci skip]
Merge pull request #13107 from chancancode/has_one_counter_cache_should_raise

Raise `ArgumentError` when `has_one` is used with `counter_cache`
Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/associations/builder/belongs_to.rb
	activerecord/lib/active_record/associations/builder/singular_association.rb
Merge pull request #13055 from dmitriy-kiriyenko/fix-segmentation-fault-it-ruby-2.0.0-p353

Fix segmentation fault in Ruby 2.0.0-p353.
Removed redundant field name in the guide

Fixes: #13108
[ci skip]
Honor to RAILS_GROUPS env variable while loading gems with Bundler
config.assets.enabled isn't used anymore to disable Rails asset pipeline
Changelog entries for changes in config/application.rb template
Merge pull request #13119 from sbagdat/patch-1

Update render with a spacer_template [ci skip]
Improve changelogs [ci skip]
Use genderless pronouns in API docs
Use genderless pronouns in security guide. [ci skip]

related  #49ff20d9b164693ed7fee880b69cc14b141678b3

Conflicts:
	guides/source/security.md
[ci skip] Removing some gender sensitive object pronouns
Update API docs guidelines with reference about gender neutral pronouns
Add examples for gender neutral pronouns
Cleanups in API docs: his => their
Update active_record_querying.md

he or she => they
Merge pull request #11466 from jetthoughts/updated_tesing_guides

Fix `rake test` description in the guides [ci skip]
`mail()` without arguments is a getter for the current mail.

This behavior is documented in our guides (http://edgeguides.rubyonrails.org/action_mailer_basics.html#action-mailer-callbacks)
but was broken in the past. This commit short curcuits
the `mail` method if:

  1. mail() was previously called
  2. no headers are passed
  3. no block is passed

Closes #13090.

/cc @pixeltrix

Conflicts:
	actionmailer/CHANGELOG.md
Merge pull request #13134 from rubiii/patch-1

added missing require to active_support/tagged_logging