add include_hidden option to collection_check_boxes helper
Save has_one associations only if record has changes

Prevents save related callbacks such as `after_commit` being
triggered when `has_one` objects are already persisted and have no
changes.
Don't load test env by default
Only use BINARY for mysql case sensitive uniqueness check when column has a case insensitive collation.
Upgraded jquery-rails gem version
A pass over the Getting Started guide sections 1, 2, and 3 [ci skip]

* Add note about managing Ruby environments
* Point to curated lists of Ruby learning resources
* Expound on DRY and Convention over Configuration
* Remove note on superuser--thankfuly coders new to Rails don't have to sudo anymore :)
* Installation/verification instructions for SQLite3, since it's a dependency
docs, mention that the current inflection rules are frozen. [ci skip]

Closes #13993.
Fix tidy_bytes for JRuby
The previous implementation was broken because JRuby (1.7.10) doesn't
have a code converter for UTF-8 to UTF8-MAC.
docs, update broken link. [ci skip]

from https://github.com/rack/rack/blob/master/lib/rack/server.rb#L289-L300.
docs, link to HTTP and CGI header definitions. [ci skip]

This was a reaction to: https://github.com/rails/rails/pull/9700#issuecomment-34550210
Merge pull request #13919 from jcoyne/fix_jruby_encoding

Fix tidy_bytes for JRuby
Avoid using deprecated arel constants
Add missing directory slashes [ci skip]
Merge pull request #14007 from kintamanimatt/missing_directory_slashes

Add missing directory slashes [ci skip]
Add tip about using RDoc's --pipe command to quickly test the output of
a piece of documentation.

This can be useful for trying out combinations of markup and code, as
discussed in rails/rails@225bcad
docs, hide inflector comment targeting only contributors. [ci skip]

This is a follow up to: https://github.com/rails/rails/commit/07c70245a128cfe42f134be8759963dc98f1a63e

As suggested by @fxn this comment should not be visible in the API:
https://github.com/rails/rails/commit/07c70245a128cfe42f134be8759963dc98f1a63e#commitcomment-5331658
Merge pull request #14008 from udaykadaboina/jqueryUpgrade

Upgraded jquery-rails gem version
Renamed session_serializer option to cookies_serializer
Just very so slightly better test coverage
Added HybridSerializer to upgrade existing marshal cookies (wip: need tests)