Log Message:
Import ruby-activemodel-4.2.8 as devel/ruby-activemodel42

Notable changes since 3.2:

- Add ActiveModel::ForbiddenAttributesProtection, a simple module to
  protect attributes from mass assignment when non-permitted attributes
  are passed.
- Added ActiveModel::Model, a mixin to make Ruby objects work with
  Action Pack out of box.
- Added new API methods reset_changes and changes_applied to
  ActiveModel::Dirty that control changes state.
- Ability to specify multiple contexts when defining a validation.
- attribute_changed? now accepts a hash to check if the attribute was
  changed :from and/or :to a given value.
- Introduced validate as an alias for valid?.
- Introduced the restore_attributes method in ActiveModel::Dirty to
  restore the changed (dirty) attributes to their previous values.
- has_secure_password no longer disallows blank passwords (i.e.
  passwords that contains only spaces) by default.
- has_secure_password now verifies that the given password is less than
  72 characters if validations are enabled.