Describes change notifiers and what they are used for.
Change notifiers allow threads to be notified of changes in the environment
such as a switch in locale, crossing over past midnight etc.; the TChanges enumerator
lists the possible events.
A change notifier is a Kernel object and, as such, is managed by the Kernel.
Access to a change notifier is through an RChangeNotifier handle.
The list of possible events is itemised by the enumerators of the TChanges enum.
The change notifier service is not used directly but is an asynchronous
service provider intended to be part of an active object. For example, the
Environment Change Notifier API provides a CEnvironmentChangeNotifier active
object which uses the services of the change notifier as part of its implementation.