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]
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