= New Features

* A dirty plugin has been added, which saves the initial value of
  the column when the column is changed, similar to
  ActiveModel::Dirty:

    artist.name                   # => 'Foo'
    artist.name = 'Bar'
    artist.initial_value(:name)   # 'Foo'
    artist.column_change(:name)   # ['Foo', 'Bar']
    artist.column_changes         # {:name => ['Foo', 'Bar']}
    artist.column_changed?(:name) # true
    artist.reset_column(:name)
    artist.name                   # => 'Foo'
    artist.column_changed?(:name) # false
    artist.update(:name=>'Bar')
    artist.column_changes         # => {}
    artist.previous_changes       # => {:name=>['Foo', 'Bar']}

* Database#create_table now respects an :as option to create a
  database based on the results of a query.  The :as option value
  should either be an SQL string or a dataset.

    DB.create_table(:new_foos, :as=>DB[:foos].where(:new=>true))

* The json_serializer and xml_serializer plugins can now serialize
  arbitrary arrays of model objects by passing an :array option
  to the to_json class method.  This works around an issue in
  ruby's JSON library where Array#to_json does not pass arguments
  given to it to the members of the array.

    Artist.to_json(:array=>[Artist[1]], :include=>:albums)

* You can now use the % (modulus) operator in the same way you
  can use the bitwise operators in Sequel:

    :column.sql_number % 1 # (column % 1)

* On PostgreSQL, you can now provide :only, :cascade, and :restart
  options to Dataset#truncate to use ONLY, CASCADE, and
  RESTART IDENTITY.  Additionally, you can now truncate multiple
  tables at the same time:

    DB.from(:table1, :table2).truncate(:cascade=>true)

* The :index option when creating columns in the schema generator
  can now take a hash of index options:

    DB.create_table(:foo){Integer :bar, :index=>{:unique=>true}}

* A Database#cache_schema accessor has been added, it can be set
  to false to have the Database never cache schema results.  This
  can be useful in Rails development mode, so that you don't need to
  restart a running server to have models pick up the new schema.

* Database#log_exception has been added for easier instrumentation.
  It is called with the exception and SQL query string for all
  queries that raise an exception.

* The Sequel.migration DSL now has a transaction method that forces
  transaction use for the given migration.

= Other Improvements

* Many theoretical thread-safety issues have been fixed for ruby
  implementations that don't use a global interpreter lock.
  Previously, Sequel relied on MRI's global interpreter lock for
  part of its thread safety, now it does manually locking in more
  places to avoid thread-safety issues on JRuby (and other ruby
  implementations without a global interpreter lock).

  No Sequel user ever reported a production error related to the
  previous thread-safety issues, and most of the issues fixed
  were so difficult to hit that even tests specifically designed
  to raise errors were unable to do so.

* Sequel.single_threaded = true now disables the mutex
  synchronization that enforces thread safety for additional
  performance in single threaded mode.

* Sequel's migrators now only attempt to use transactions by
  default if the underlying database supports transactional DDL.
  SQLite does support transactional DDL, but Sequel will not
  use transactions for SQLite migrations as it causes issues
  when emulating alter_table operations for tables with foreign
  keys.

* Errors that occur when rolling back database transactions are
  now handled correctly.  Previously, the underlying exception was
  raised, it wasn't correctly wrapped in a Sequel::DatabaseError,
  and if it was due to a database disconnection, the connection
  wasn't removed from the pool.

* Sequel no longer sets ruby instance variables on java objects,
  fixing warnings on JRuby 1.7 and attempting to be forward
  compatible with JRuby 2.0.

* Sequel now uses date and timestamp formats that are multilanguage
  and not DATEFORMAT dependent on Microsoft SQL Server.

* Sequel now correctly escapes blackslash-carriage return-line feed
  on Microsoft SQL Server.

* Parsing the column default values in the oracle adapter no longer
  requires database superuser privileges.

* Sequel now correctly handles parsing schema for tables in other
  databases on MySQL.  Previously, it would always look in the
  current database.

* Sequel no longer doubles backslashes in strings by default.  It
  now only does so on MySQL, since that is the only database that
  appears to use backslashes for escaping.  This fixes issues with
  backslashes being doubled on some of the less commonly used
  adapters.

* The pg_auto_parameterize extension now works correctly when
  using cursors.

* Dataset#truncate now raises an Error if you attempt to do so
  on a dataset that uses HAVING.  Previously, it only checked for
  WHERE.

* The schema dumper now recognized the identity type.

= Backwards Compatibility

* Association reflections now store cached information in a
  separate subhash due to the thread-safety changes.  Any code
  accessing an association reflection should always call the
  related method to get the cached data instead of checking
  for a specific location in the hash.

* Association reflection internals for many_through_many associations
  changed significantly, any code that accesses the edge information
  in the reflection will need to be changed to use the new methods
  instead of accessing the old values directly.

* The features deprecated in 3.34.0 have now been removed:
  * Ruby <1.8.7 support
  * PostgreSQL <8.2 support
  * Dataset#disable_insert_returning on PostgreSQL
  * Array#all_two_pairs? and #sql_expr_if_all_two_pairs
  
