Added test to ensure that DescendantsTracker does not leak memory on singleton classes
Change ActionController::Parameters#require behavior when value is empty
When the value for the required key is empty an ActionController::ParameterMissing is raised which gets caught by ActionController::Base and turned into a 400 Bad Request reply with a message in the body saying the key is missing, which is misleading.

With these changes, ActionController::EmptyParameter will be raised which ActionController::Base will catch and turn into a 400 Bad Request reply with a message in the body saying the key value is empty.
Fix doc in Postgres database creation
add active model basics wip to guides/documents.yaml
support :unless_exist for FileCache
allow to test AR master against AR-JDBC master (with `ENV['AR_JDBC']`)
`export AR_JDBC=true` on travis-ci as a *before_install* (but on jruby only)
Moved all JSON core extensions into core_ext/object/json

TL;DR The primary driver is to remove autoload surprise.

This is related to #12106. (The root cause for that ticket is that
json/add defines Regexp#to_json among others, but here I'll reproduce
the problem without json/add.)

Before:

   >> require 'active_support/core_ext/to_json'
   => true
   >> //.as_json
   NoMethodError: undefined method `as_json' for //:Regexp
     from (irb):3
     from /Users/godfrey/.rvm/rubies/ruby-2.0.0-p195/bin/irb:16:in `<main>'
   >> //.to_json
   => "\"(?-mix:)\""
   >> //.as_json
   => "(?-mix:)"

After:

   >> require 'active_support/core_ext/to_json'
   => true
   >> //.as_json
   => "(?-mix:)"

This is because ActiveSupport::JSON is autoloaded the first time
Object#to_json is called, which causes additional core extentions
(previously defined in active_support/json/encoding.rb) to be loaded.

When someone require 'active_support/core_ext', the expectation is
that it would add certain methods to the core classes NOW. The
previous behaviour causes additional methods to be loaded the first
time you call `to_json`, which could cause nasty surprises and other
unplesant side-effects.

This change moves all core extensions in to core_ext/json. AS::JSON is
still autoloaded on first #to_json call, but since it nolonger
include the core extensions, it should address the aforementioned bug.

*Requiring core_ext/object/to_json now causes a deprecation warnning*
Add params option for button_to

The parameters are rendered as hidden form fields within the generated
form. This is useful for when a record has multiple buttons associated
with it, each of which target the same controller method, but which
need to submit different attributes.
Renamed generated_feature_methods to generated_association_methods.
Let validates_inclusion_of accept Time and DateTime ranges

fixes 4.0.0 regression introduced in 0317b93c17a46d7663a8c36edc26ad0ba3d75f85
Merge pull request #12612 from amatsuda/amo_validates_inclusion_of_time_range_error

Let validates_inclusion_of accept Time and DateTime ranges
[ci skip] second parameter of asset-url is depricated
Merge pull request #12617 from skv-headless/master

[ci skip] second parameter of asset-url is deprecated
Fix the install task
Correct error in Utils.normalize_path that changed paths improperly
Merge pull request #12619 from Veraticus/fix_utils_normalize_path

Correct error in Utils.normalize_path that changed paths improperly
pass app config to controller helper proxy

After this fix application config become available when calling helper outisde of view

config/application.rb

    #...
    config.asset_host = 'http://mycdn.com'
    #...

Somewhere else

    ActionController::Base.helpers.asset_path('fallback.png')
    # => http://mycdn.com/assets/fallback.png
Merge pull request #12622 from timsly/helpers-from-outside

pass app config to controller helper proxy
slice! should not remove default hash value/proc