This caused a bug with the new associations implementation, because now
association conditions are represented as Arel nodes internally right up
to when the whole thing gets turned to SQL.

In Rails 3.2, association conditions get turned to raw SQL early on,
which prevents Relation#merge from interfering.

The current implementation was buggy when a default_scope existed on the
target model, since we would basically end up doing:

  default_scope.merge(association_scope)

If default_scope contained a where(foo: 'a') and association_scope
contained a where(foo: 'b').where(foo: 'c') then the merger would see
that the same column is representated on both sides of the merge and
collapse the wheres to all but the last: where(foo: 'c')

Now, the RHS of the merge is left alone.

Fixes #8990

because of an ambiguous column name. This happened if the association
model had a default scope that referenced a third table, and the third
table also referenced the original table (with an identical
foreign_key).

Mysql requires that ambiguous columns are deambiguated by using the full
table.column syntax. Postgresql and Sqlite use a different syntax for
updates altogether (and don't tolerate table.name syntax), so the fix
requires always including the full table.column and discarding it later
for Sqlite and Postgresql.

`Kernel.quietly` silences `STDOUT` and `STDERR`, which is useless if
the logger is writing to a file, while `AS::Logger#silence` swaps the
logger level to `ERROR`.

Related to #8820 and #8052.

With the addition of String#in_time_zone and Date#in_time_zone
we can simplify the type casting code by checking if the value
has an `in_time_zone` method.

Previously, when `time_zone_aware_attributes` were enabled, after
changing a datetime or timestamp attribute and then changing it back
to the original value, `changed_attributes` still tracked the
attribute as changed. This caused `[attribute]_changed?` and
`changed?` methods to return true incorrectly.

Example:

    in_time_zone 'Paris' do
      order = Order.new
      original_time = Time.local(2012, 10, 10)
      order.shipped_at = original_time
      order.save
      order.changed? # => false

      # changing value
      order.shipped_at = Time.local(2013, 1, 1)
      order.changed? # => true

      # reverting to original value
      order.shipped_at = original_time
      order.changed? # => false, used to return true
    end

closes #6865

or the ConnectionPool silently fails to close connections inside the Thread

Travis only has PostgreSQL 9.1.x but 9.2 is required for range datatypes.

This reverts commit e9d2ad39.

Closes #8460

Conflicts:
	activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
	activerecord/test/cases/dirty_test.rb

[ci skip]

Refactored transaction state into its own object. Each transaction creates a new transaction state object upon initialization.

* User class instead of Users.
* #where_values_hash does not change the value to downcase as the
  example was showing.

[ci skip]

This reverts commit 637a7d9d, reversing
changes made to 5937bd02.

Suggested by @dhh.

It doesn't affect the generated SQL, so seems reasonable to continue to
allow it as an association option.

Fixes #8795

I think that these signs are probably mistake.

This revision makes crystal clear that the methods go
straight to the database and update the receiver. It
also adds and example, and removes the duplication
in the singular and plural forms by referring one to
the other.

There's no need to create a new arel table or reflect on the column
association if the value is empty, these attributes are not used.

Also no need to concat a new array, just append the query value.

If we set encoding latin1 for a PostgreSQL database, it calls
PostgreSQLAdapter::create_database with options that have,
among other things:

  { 'encoding' => 'latin1' }

Then, we use reverse_merge(:encoding => "utf8") to setup the default
encoding. In the end, the hash looks like:

  { :encoding => 'utf8', 'encoding' => 'latin1' }

The call to options.symbolize_keys calls to_sym on each_key of this
Hash. It usually means that the encoding passed overwrites the default
utf8, but it's not guaranteed. So, we shouldn't rely on it.

The same was happening in ActiveRecord::ConnectionHandling.

This reverts commit 8348f9ea, reversing
changes made to 9dfe2d6f.

Reason: this broke railties tests as explained in the issue, and the
author is going to review and report back.

https://github.com/rails/rails/pull/8930#issuecomment-12272671

We were previously rescuing "nil" when no exception class was found.
This does work in 1.9.3, but does not in 2.0, raising an exception
asking for a class or module to be given to the rescue clause.

Thanks @yahonda for catching this.