Move the private method #extract_schema_and_table into a separate
Utils module so that it can be tested without resorting to #send.

This caused that `find_each` was producing extra db call taking all the records from db, and was less efficient than `ActiveRecord::Base#all`.

when condtions references tables from includes.
Test fail because of invalid sql:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: comments.id:
SELECT "posts".id FROM "posts" INNER JOIN "readers" ON "posts"."id" = "readers"."post_id"
WHERE "readers"."person_id" = 1 AND (comments.id is null)

Bug described in github#925

This commit will revert fix from https://github.com/rails/rails/commit/3436fdfc12d58925e3d981e0afa61084ea34736c , but tests is ok.

Bug described in #6569 ticket.

In order make Relation behavior closer to Array
Made Relation#sum to accept block and delegate it to Array#sum

In order to make CollectionAssociation behave closer to Array
Add the ability to pass block to #find method just like Array#find does.

The changes broke bulk migration tests and were fixed in 4d256bc6;
however that brought back the issue of #1857 and so this commit goes
back to the original scenario and just adds change_table to the list
of methods which are to be recorded in the CommandRecorder. The
method_missing now delegates all calls to the underlying connection as
before.

Assign the association attributes to the associated record before the before_initialize callback of the record runs. Fixes #1842.

CommandRecorder should delegate in method_missing where possible. Fixes some tests in migration_test.rb under mysql. The problem was introduced in c278a2c5.

Use latest Arel syntax and pass each order by expression as separate argument to order method as otherwise invalid Oracle SQL is generated.

default create_with_value to a hash so we can eliminate conditionals, add test surrounding create_with(nil) behavior

record unsupported methods in CommandRecorder instead of letting the unsupported methods go through to the underlying db causing errors like duplicate columns to occur when rolling back migrations

* Only on postgresql, order("first asc, second asc") was invalid
* Closes #1720

* amongst other things, allows meta_search to run against view-backed models

Fix inconsistencies by being polite to the wrapped body. Needed for Rack::Sendfile to function properly. See issue #1761.

Changed the default value for the options argument on ActiveRecord::ConnectionAdapters::Table#column_exists? from nil to an empty Hash {}.

That method calls through to ActiveRecord::ConnectionAdapters::SchemaStatements##column_exists? expects options to be a Hash.

When options was nil, an error would occur in cases where the column did exist because the called method attempted to perform a key lookup on options.

Add support for using an ARCONFIG environment variable to specify the location of the config.yml file for running the tests

Make assert_no_queries literally enforce that there are no queries. As in, not a single line of SQL should be sent to the database, not even stuff that is ignored by assert_queries. The argument being that if you write assert_no_queries, you really do not want there to be any queries.

Don't wrap operations on collection associations in transactions when they are not needed, so the connection adapter does not send empty BEGIN COMMIT transactions blocks to the database.

* add/cleanup tests

* tidy test code and fix my typo 

* table_exists? scoped by schema search path unless schema is explicitly named. Added tests and doc to clarify the behaviour
* extract_schema_and_table tests and implementation extended to cover all cases
* primary_key does not ignore schema information
* add current_schema and schema_exists? methods
* more robust table referencing in insert_sql and sql_for_insert methods