docs, Cookie values are String based. Closes #12860. [ci skip]
Rely on backticks instead of tt tags [ci skip]

Since the language in code blocks is inferred, if the code contains tt
tags, the block will be parsed as XML for instance while it is Ruby.
context in validation goes through has many relationship
Updated the cookie docs to use the safer JSON.{generate,parse}

cc @senny
Add test case for autosave HasMany with accepts_nested_attributes.

It should not save the parent record when the nested attributes are
invalid.

Test case to cover #8194.
Merge pull request #13974 from laurocaetano/test_case_for_autosave_with_accepts_nested_attributes

Add test case for autosave association with nested attributes.
Fixed an issue where reloading of removed dependencies would cause an unexpected circular dependency error
Skips tests on Windows that create files with illegal characters
Merge pull request #13977 from Octember/master

Fixed an issue where reloading of removed dependencies would cause an un...
Merge pull request #13979 from mellowi/windows_disallowed_static_files_skipped

Skips tests on Windows that create files with illegal characters
Skips linked folder tests if symlink is invalid
Merge pull request #13980 from mellowi/skipping_linked_folder_tests_if_symlink_is_invalid

Skips linked folder tests if symlink is invalid
Merge pull request #13978 from Fortisque/kevin/validation_context_for_children

context in validation goes through has many relationship
Reaper has access to threadsafe active? call
Remove outdated TODO from url_for test, this test was fixed in 900a2d30
Merge pull request #13981 from Fortisque/kevin/postgresql_reaper_threadsafe

Reaper has access to threadsafe active? call
use feature detection to decide which implementation to use

Decouple the code from the particular Ruby version.
use File.exist? instead of File.exists?
Merge pull request #13983 from hsbt/remove-warning

use File.exist? instead of File.exists?
FilterParameters is referenced at the class level from the Request

Since it's already required in the file, we don't need to use autoload
too. This commit is symmetrical change to 0b10180 for Response.