Log Message:
Update ruby-sequel to 4.30.0.

= New Features

* Overriding the :limit and :eager_limit_strategy association options
  can now be done on a per-call basis when eager loading, by using an
  eager block callback and setting the :eager_limit or
  :eager_limit_strategy dataset options. Example:

    Album.eager(:tracks=>proc{|ds| ds.clone(:eager_limit=>5)}).all

* Dataset#insert_conflict and #insert_ignore have been added on
  SQLite, adding support for the INSERT OR ... SQL syntax:

    DB[:table].insert_ignore.insert(:a=>1, :b=>2)
    # INSERT OR IGNORE INTO TABLE (a, b) VALUES (1, 2)

    DB[:table].insert_conflict(:replace).insert(:a=>1, :b=>2)
    # INSERT OR REPLACE INTO TABLE (a, b) VALUES (1, 2)

* An identifier_columns plugin has been added, which allows
  Sequel::Model#save to work when column names contain double
  underscores.

= Other Improvements

* IPv6 addresses can now be used in connection URLs when using
  ruby 1.9.3+.

* The :db_type entries in column schema hashes now include sizes
  for string and decimal types on DB2 and when using the jdbc
  adapter's generic schema parsing.

* Database#row_type in the pg_row extension now handles different
  formats of specifying schema qualified types.  So a row type
  registered via :schema__type can be found using
  Sequel.qualify(:schema, :type).

* Another disconnect error is recognized in the tinytds adapter.