= Improvements

* Database#copy_into in the jdbc/postgresql adapter now works
  correctly when using multibyte characters in strings.

* The alter_table add_foreign_key method is now reversible when the
  :foreign_key_constraint_name option is used.

* The jdbc/h2 and jdbc/hsqldb adapters now respect the
  :foreign_key_constraint_name option.

* Calling Model.freeze on an already frozen model no longer raises
  an error.

* An unnecessary database query is now avoided when loading the
  pg_inet extension when the pg_array extension is already loaded.

* A better exception message is now used when migrating with an
  empty migration directory.

= Backwards Compatibility

* Model.allowed_columns has been removed. Use the whitelist_security
  plugin if you want to call it.

* Model use_after_commit_rollback class and instance accessors have
  been removed.

* Support for the Model#_before_validation method has been removed.

* The private Model.plugin_module_defined? method has been removed.
