remove the new metadata note in Rails 4 upgrade guide

this was pulled out of Rails 4, see rails/rails#8399 for the discussion
Unprepared Visitor + unprepared_statement
Some copy edit and formatting for upgrading guide.
Merge pull request #9553 from neerajdotname/7365-mergin-scopes-and-where

7365 merging scopes for where clauses
Write a more comprehensive CHANGELOG message [ci skip]
Update test name to reflect change in how scopes merging works

Introduced in f1082b8588a9144eedb34d511f0074031f692d98.
Full changelog in 9f007d7fe5f90257c71baa2c4e7c76fb44512986.

[ci skip]
Merge pull request #9609 from arunagw/using-latest-arjdbc

Using latest AR-JDBC for JRuby
Merge pull request #8966 from cfabianski/disable_prepared_statement_when_preparing_a_query

Unprepared Visitor + unprepared_statement

Conflicts:
	activerecord/CHANGELOG.md
Merge pull request #8868 from tehgeekmeister/master

Use the index name explicitly provided in a migration when reverting.

Fixes #8868

Conflicts:
	activerecord/CHANGELOG.md
Explained how merging of scope works
fixing typo in the merging scopes section
Fix rails console --sandbox

I've also added a proper acceptance test which reproduced the issue.

Closes #9513, #9515.
Refactored test case with standard variable naming
Merge pull request #9611 from choudhuryanupam/master

Refactored test case with standard variable names
Merge pull request #9497 from route/subclass_from_attrs

Fix ActiveRecord `subclass_from_attrs` when eager_load is false.

Conflicts:
	activerecord/CHANGELOG.md
Avoid short-circuit return
Make sure options is a hash
The console --sandbox transaction should not be joinable

Thanks @neerajdotname for noticing this bug.
Fix changelog indent, remove self from method call in changelog/doc examples

[ci skip]
Refactored nested associations so they are more readable. Added comments
which make it clearer about what's going on.