= New Features

* Model.dataset_module has been added for easily adding methods to
  a model's dataset:
  
    Album.dataset_module do
      def with_name_like(x)
        filter(:name.like(x))
      end
      def selling_at_least(x)
        filter{copies_sold > x}
      end
    end
    Album.with_name_like('Foo%').selling_at_least(100000).all
    
  Previously, you could use def_dataset_method to accomplish the
  same thing.  dataset_module is generally cleaner, plus you are
  using actual methods instead of blocks, so calling the methods
  is faster on some ruby implementations.

* Sequel now uses a Sequel::SQLTime class (a subclass of Time) when
  dealing with values for SQL time columns (which don't have a date
  component).  These values are handled correctly when used in
  filters or insert/update statements (using only the time
  component), so Sequel can now successfully round trip values for
  time columns.  Not all adapters support returning time column
  values as SQLTime instances, but the most common ones do.

* You can now drop foreign key, primary key, and unique constraints
  on MySQL by passing the :type=>(:foreign_key|:primary_key|:unique)
  option to Database#drop_constraint.

* The ODBC adapter now has initial support for the DB2 database, use
  the :db_type=>'db2' option to load the support.

= Other Improvements

* The mysql2 adapter now uses native prepared statements.

* The tinytds adapter now uses uses sp_executesql for prepared
  statements.

* DateTime and Time objects are now converted to Date objects when
  they are assigned to a date column in a Model instance.
  
* When converting a Date object to a DateTime object, the resulting
  DateTime object now has no fractional day components.  Previously,
  depending on your timezone settings, it could have had fractional
  day components.

* The mysql2 adapter now supports stored procedures, as long as they
  don't return results.
  
* Mass assignment protection now handles including modules in model
  classes and extending model instances with modules.  Previously, if
  you defined a setter method in a module, access to it may have been
  restricted.
  
* The prepared_statements_safe plugin now works on classes without
  datasets, so you can now do the following to load it for all models:
  
    Sequel::Model.plugin :prepared_statements_safe
    
* Dataset#hash now works correctly when handling SQL::Expression
  instances.
  
* Model#hash now correctly handles classes with no primary key or with
  a composite primary key.
  
* Model#exists? now always returns false for new model objects.

= Backwards Compatibility

* If you were previously setting primary key values manually for new
  model objects and then calling exists? to see if the instance is
  already in the database, you need to change your code from:
  
    model.exists?
    
  to:
  
    model.this.get(1).nil?
