It was supposed to be removed by the preceding two reversions but I did
them in the wrong order.

This reverts commit 5d528f83.

Relates to f8c8ad56 which is also getting reverted due to failing test.

This reverts commit c321b309.

Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
	activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

Reason: failing test

  1) Error:
test_valid_column(ActiveRecord::ConnectionAdapters::SQLite3AdapterTest):
NoMethodError: undefined method `column' for
    test/cases/adapters/sqlite3/sqlite3_adapter_test.rb:29:in
`test_valid_column'

This reverts commit 8aa4603a.

Reverting the revert because I reverted the wrong thing! Fail.

This reverts commit 1fc6876b, reversing
changes made to 0268b5d8.

Reason: failing test

  1) Error:
test_valid_column(ActiveRecord::ConnectionAdapters::SQLite3AdapterTest):
NoMethodError: undefined method `column' for
    test/cases/adapters/sqlite3/sqlite3_adapter_test.rb:29:in
`test_valid_column'

closes #8423.

conversion of boolean types (true => 1 and false => 0). If the numeric value
being assigned is a BigDecimal, then ActiveRecord compares a BigDecimal to
true and false. This is known to be very slow in Ruby 1.9.3.

Allow store accessors to be overrided like other attribute methods,
e.g.:

    class User < ActiveRecord::Base
      store :settings, accessors: [ :color, :homepage ], coder: JSON

      def color
        super || 'red'
      end
    end

Describe better the changes related to raising errors with empty
array/hash values in where clauses.

[ci skip]

Travis failed because the postgresql version installed there does not
support extensions, so we just need to skip this for now.

There is no need to create the extension in the database just to test if
it's dumped, we can stub that instead.

When extensions are supported but there's no one enabled in the
database, we should not print anything related to them in schema.rb.

[ci skip]

add ActiveRecord::AbstractAdapter#extensions and ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#extensions to allow dumping of enabled extensions to schema.rb, add ActiveRecord::SchemaDumper#extensions to dump extensions to schema.rb

improve tests to check for existence of extensions method, and skip testing dumped extensions if they are unsupported by the database

So that they are printed nicely on GitHub.