to address ORA-01400 errors with Oracle enhanced adapter.

The original commit 3c0bf043 requires :json_data_empty attribute
has empty string OR null, then setting `:default => ""` is enough.

to address ORA-01400 errors with Oracle enhanced adapter.

Issue #4856 had been fixed and tested with
the attribute `:null => false, :default => ""`.
Now `:null => false` attribute is not necessary to test this issue.

to make store works all database adapters.

Issue #6115 has been fixed and tested with
the attribute `:null => false, :default => ""`
However `:null => false` attribute is not necessary to test this issue,
which causes many ORA-01400 errors with Oracle enhanced adapter.

This commit needs to be reverted because it introduces difficulties when
using sqlite3 in development and other databases in production. This
happens because when you create time column in sqlite3, it's dumped as
datetime in schema.rb file.

This reverts commit 57d534ee, reversing
changes made to 20f049fb.

Conflicts:

	activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

Improve the derivation of HABTM join table name to take account of nesting.
It now takes the table names of the two models, sorts them lexically and
then joins them, stripping any common prefix from the second table name.

Some examples:

  Top level models
  (Category <=> Product)
  Old: categories_products
  New: categories_products

  Top level models with a global table_name_prefix
  (Category <=> Product)
  Old: site_categories_products
  New: site_categories_products

  Nested models in a module without a table_name_prefix method
  (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: categories_products

  Nested models in a module with a table_name_prefix method
  (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: admin_categories_products

  Nested models in a parent model
  (Catalog::Category <=> Catalog::Product)
  Old: categories_products
  New: catalog_categories_products

  Nested models in different parent models
  (Catalog::Category <=> Content::Page)
  Old: categories_pages
  New: catalog_categories_content_pages

Also as part of this commit the validity checks for HABTM assocations have
been moved to ActiveRecord::Reflection One side effect of this is to move when
the exceptions are raised from the point of declaration to when the association
is built. This is consistant with other association validity checks.

Modify test schema.rb to use a VARCHAR rather than a TEXT when a default is required to keep MySQL happy.

Overriding implementation can call super.

Remove extra attributes from HABTM join tables in AR tests

If a model belongs_to two associations with the same class, then reset_counters
will reset the wrong counter cache.

Finding the right reflection should use the foreign_key instead, which should
be unique.

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.

This is the 'top level' connection, inherited by any models that include
ActiveRecord::Model or inherit from ActiveRecord::Base.

Previously we would just silently write the attribute. This can lead to
subtle bugs (for example, see the change in AutosaveAssociation where a
through association would wrongly gain an attribute.

Also, ensuring that we never gain any new attributes after
initialization will allow me to reduce our dependence on method_missing.

Test polymorphic record with optimistic locking and counter cache should be destoyed without catching the ActiveRecord::StaleObjectError.

fix behavior when after_initialize is defined and a block is passed to Base.create

CollectionAssociation#merge_target_lists should write to the underlying attributes when copying, rather than using the assignment method

Add test to specify that attributes from an association's conditions should be assigned without mass-assignment protection when a record is built on the association.

singular and collection relations in AR can now specify mass-assignment security options (:as and :without_protection) in build, create and create! methods.