add test to show offset query_methods on mysql & mysql2

change test to cover public API

Under Rails 3.1, you were allowed to pass a hash to a find_or_create
method with multiple attribute names, but this was broken as the
arguments were being improperly validated.

See the CHANGELOG for details.

Fixes #950.

This reverts commit c99d507f.

Fixes issue #3483, regarding using a mixture of ranges and discrete values in find conditions. Paired with Joey Schoblaska.

The previous behavior was unintentional, and some people was relying on it. Now the dynamic finder will always expecting the number of arguments to be equal or greater (so you can still pass the options to it.)

So if you were doing this and expecting the second argument to be nil:

    User.find_by_username_and_group("sikachu")

You'll now get `ArgumentError: wrong number of arguments (1 for 2).` You'll then have to do this:

    User.find_by_username_and_group("sikachu", nil)

having raises NoMethodError: undefined method `empty?' when a Fixnum or Date/Time were passed via varargs

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.

if a query contains a limit or an offset, ActiveRecord::FinderMethods#find_last had inconsistent behavior.

If the records were loaded, it returned the last record in the cached list.
If they were not, it reversed the order of the query and changed the limit to one.
If the earlier limit was less than the total matching the query in the db,
it would return a different record than if the records had been cached.

This commit changes find_last so that it loads the records when getting the
last record on a query containing a limit or an offset, which makes the behavior consistent.

value on a selected field.

Return nil from read_attribute(:foo) if 'foo' is not present in the @attributes hash, but the _foo method has been defined. This brings the behaviour into line with the 3-0-stable branch and the master branch before 93641ed6 (there were previously no assertions about this which is why the change slipped through). Note that actually calling the 'foo' method will still raise an error if the attribute is not present.