Merge pull request #10145 from wangjohn/instrumentation_registry_creation

Consolidating thread locals in AS::Notifications
JoinPart is no longer an abstract class
fix AP warning; remove unused variable
Merge pull request #10147 from vipulnsward/fix_AP_live_warning

fix AP warning; remove unused variable
change array of array to hash
Merge pull request #10148 from vipulnsward/traces_change

change array of array to hash
Merge pull request #10138 from hbakhtiyor/test-dirs-environment

Add TEST_DIRS enviroment for constrain test directories in rakefile
changed variable name active_record => base_klass

Current code stores the klass name in active_record and this
is used throughout. While reviewing the code time and again
I had the mental picture of active_record being an instance of
a klass. However here the actual klass is being stored in
@active_record.

Secondly at two different places while referring to @active_record
the comment refers to it as base klass. All this points to
active_record being not the best variable name.

So I thought it is better to replace active_record with base_klass.

This change is confined to JoinDependency, JoinBase, JoinPart and
JoinAssociation - all joining related work.
Merge pull request #135 from dalton/master

Change user_class to author_class in Engine guide
Merge pull request #10151 from neerajdotname/ar-to-klass

changed variable name active_record => base_klass
Merge pull request #10142 from wangjohn/grouping_thread_locals

Delegating the value getter and setters in the ScopeRegistry
Removed unused setup
Merge pull request #10153 from choudhuryanupam/master

Removed unused setup
Fix typo
Merge pull request #9843 from indirect/rails_bin

Rails 4 prints help for "rails new" when running "rails console"
get the Action Mailer guide ready. [ci skip]
copy-edit pass in AM changelog [ci skip]
improve accuracy of simple_format documentation. span doesn't get sanitized.
Use camelize instead of capitalize on error screen
Merge pull request #10103 from senny/get_action_mailer_guide_ready_for_prime_time

Get Action Mailer guide ready for prime time [ci skip]