= New Features

* A pg_xmin_optimistic_locking plugin has been added.  This plugin
  uses PostgreSQL's xmin system column to implement optimistic
  locking.  The xmin system column is automatically updated whenever
  the database row is updated.  You can load this plugin into a
  base model and have all models that subclass from it use optimistic
  locking, without needing any user-defined lock columns.

= Other Improvements

* set_column_allow_null is now a reversible migration method inside
  alter_table blocks.

* The use of ILIKE no longer forces the ESCAPE clause on PostgreSQL,
  which allows the use of ILIKE ANY and other constructions.  There
  is no need to use the ESCAPE clause with ILIKE, because the value
  Sequel uses is PostgreSQL's default.

* The xid PostgreSQL type is now recognized as an integer type in the
  jdbc/postgresql adapter.
