Fix bad test order dependency between LoadAllFixturesTest#test_all_there and FoxyFixturesTest#test_ignores_belongs_to_symbols_if_association_and_foreign_key_are_named_the_same

Stubbing ENV[] is not safe outside MRI. At some point after the
stubbing has occurred a backtrace is printed to the ActiveSupport
warning log: there Rubinius accesses ENV['RBX_NOCOLOR'] to determine
if it should print the backtrace with colors or not, causing the
stub to fail. Other implementations might access ENV in a different
way too, we just can't predict it.
The only thing we can do here is to actually set the ENV with what
we want and restore it afterwards.

Allows you to change your configuration for calls to
`table_name_prefix`, `table_name_suffix`, and `pluralize_table_names`.
The default configuration is still ActiveRecord::Base, but you are now
able to change the configuration easily.

Also, constantizing the default_fixture_model_name when it gets loaded
in from the file. Later, when the class_name is passed to a new
FixtureSet, a deprecation warning will occur if the class_name is a
string.

As you can also configure your database connection using `ENV["DATABASE_URL"]`,
the fixture setup can't reply on the `.configurations` Hash.

As the fixtures are only loaded when ActiveRecord is actually used
(`rails/test_help.rb`) it should be safe to drop the check for an existing configuration.

This allows end-users to have a `connection` method on their models
without clashing with ActiveRecord internals.

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

Rename `ActiveRecord::Fixtures` class to `ActiveRecord::FixtureSet`.  Instances of this class normally hold a collection of fixtures (records) loaded either from a single YAML file, or from a file and a folder with the same name.  This change make the class name singular and makes the class easier to distinguish from the modules like `ActiveRecord::TestFixtures`, which operates on multiple fixture sets, or `DelegatingFixtures`, `::Fixtures`, etc., and from the class `ActiveRecord::Fixture`, which corresponds to a single fixture.

This reverts commit 7381596e.

create_fixtures should accept symbol keys for custom table -> class mappings. Fixes an unintended regression.

setup_fixture_accessors should accept symbols for table names. Fixes an unintended (and untested) regression.

Test using fixtures with random names and model names, that is not following naming conventions but using set_fixture_class instead.

It is expected that the table name be defined in the model, but this is not explicitly tested here.  This will need to be fixed.

Make sure the table name of a model is reset in a test case after assigning ActiveRecord::Base.table_name_prefix and ActiveRecord::Base.table_name_suffix.

This reverts commit f8e484d0, reversing
changes made to fa5adfb1.

Reason: broke the postgres tests.

Make sure the table name of a model is reset in a test case after assigning ActiveRecord::Base.table_name_prefix and ActiveRecord::Base.table_name_suffix.  This was somebody else's test case, so an independent opinion on the change can be helpful.

Use broken YAML that will fail with Syck as well as Psych. Fixes test_broken_yaml_exception in fixtures_test.rb on Ruby 1.8.7.

Cherry-pick from 3-1-stable: b8d46924

You can use multiple databases in your tests without disabling transactional fixtures.

Quote these dates to prevent intermittent test failure. Suppose local time is 00:50 GMT+1. Without the quoting, the YAML parser would parse this as 00:50 UTC, into the local time of 01:50 GMT+1. Then, it would get written into the database in local time as 01:50. When it came back out the UTC date from the database and the UTC date of two weeks ago would be compared. The former would be 23:50, and the latter would be 00:50, so the two dates would differ, causing the assertion to fail. Quoting it prevents the YAML parser from getting involved.

Quote these dates to prevent intermittent test failure. Suppose local time is 00:50 GMT+1. Without the quoting, the YAML parser would parse this as 00:50 UTC, into the local time of 01:50 GMT+1. Then, it would get written into the database in local time as 01:50. When it came back out the UTC date from the database and the UTC date of two weeks ago would be compared. The former would be 23:50, and the latter would be 00:50, so the two dates would differ, causing the assertion to fail. Quoting it prevents the YAML parser from getting involved.

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.