Fix habtm reflection
Conflicts:
    activerecord/CHANGELOG.md
    activerecord/lib/active_record/counter_cache.rb
    activerecord/lib/active_record/reflection.rb
    activerecord/test/cases/reflection_test.rb

Also add a Changelog entry

[related #9702]
[fixes #8928]

cache.

There is no reason for the PG adapter to have a default limit of 255 on :string
columns. See this snippet from the PG docs:

    Tip: There is no performance difference among these three types, apart
    from increased storage space when using the blank-padded type, and a
    few extra CPU cycles to check the length when storing into a
    length-constrained column. While character(n) has performance
    advantages in some other database systems, there is no such advantage
    in PostgreSQL; in fact character(n) is usually the slowest of the
    three because of its additional storage costs. In most situations text
    or character varying should be used instead.

Currently `scope_chain` uses same array for building different
`scope_chain` for different associations. During processing
these arrays are sometimes mutated and because of in-place
mutation the changed `scope_chain` impacts other reflections.

Fix is to dup the value before adding to the `scope_chain`.

Fixes #3882.

The comment in the test pretty much summarizes the issue.
`FIXME these assertions bust a lot`

Adding any type of association in class `Firm` will break this test.

I removed some deprecated stuff and this test failed.

I do not think this test provides any useful value. First of all who
counted last that 39 is the right number of associations.

Secondly there are a large number of tests which depend on reflection
returning right information about associations. Those tests will start
failing if there is a bug in the code.

Due to commit 0123c39f, column
topic.unique_replies_count has been added, and these test started to
fail since the tests depends on the topic tables column info.

This reverts commit 3803fcce.

Conflicts:
	activerecord/CHANGELOG.md

It will be deprecated only in 4.0, and removed properly in 4.1.

This reverts commit 14fc8b34.

Reason: we need to discuss a better path from this removal.

Conflicts:
	activerecord/lib/active_record/reflection.rb
	activerecord/test/cases/base_test.rb
	activerecord/test/models/developer.rb

This feature adds a lot of complication to ActiveRecord for dubious
value. Let's talk about what it does currently:

class Customer < ActiveRecord::Base
  composed_of :balance, :class_name => "Money", :mapping => %w(balance amount)
end

Instead, you can do something like this:

    def balance
      @balance ||= Money.new(value, currency)
    end

    def balance=(balance)
      self[:value] = balance.value
      self[:currency] = balance.currency
      @balance = balance
    end

Since that's fairly easy code to write, and doesn't need anything
extra from the framework, if you use composed_of today, you'll
have to add accessors/mutators like that.

Closes #1436
Closes #2084
Closes #3807

See the CHANGELOG for details.

Fixes #950.

This is to avoid confusing newbies, and to be consistent with the fact
that other options like :foreign_key already allow a symbol or a string.

Building the conditions of a nested through association could
potentially modify the conditions of the through and/or source
association.

This is a Bad Thing.

An association between two models cannot be made if a relevant key is
unknown, so fail fast rather than generating invalid SQL. Fixes #3207.

Closes #3104.

Refactor Active Record test connection setup. Please see the RUNNING_UNIT_TESTS file for details, but essentially you can now configure things in test/config.yml. You can also run tests directly via the command line, e.g. ruby path/to/test.rb (no rake needed, uses default db connection from test/config.yml). This will help us fix the CI by enabling us to isolate the different Rails versions to different databases.

Fix problem with loading polymorphic associations which have been defined in an abstract superclass. Fixes #552.

Rename Reflection#through_reflection_chain and #through_options to Reflection#chain and Reflection#options as they now no longer relate solely to through associations.

Push source_type and polymorphic conditions out of ThroughAssociation and JoinDependency::JoinAssociation and into the reflection instead.

Construct an actual ActiveRecord::Relation object for the association scope, rather than a hash which is passed to apply_finder_options. This allows more flexibility in how the scope is created, for example because scope.where(a, b) and scope.where(a).where(b) mean different things.

Implement deprecated version of AssociationReflection#primary_key_name, which has been renamed to #foreign_key. Also bumping the deprecation_horizon in Active Support to 3.1.

Rename AssociationReflection#primary_key_name to foreign_key, since the options key which it relates to is :foreign_key

Improved strategy for updating a belongs_to association when the foreign key changes. Rather than resetting each affected association when the foreign key changes, we should lazily check for 'staleness' (where fk does not match target id) when the association is accessed.