Bug 126414 [Commands] handlers: Provide help context ids
For commands and handlers to replace actions, they need to be capable of providing help context identifiers. For an example, see OpenResourceHandler in org.eclipse.ui.ide. This help context id will need to be definable through XML and through code.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
return returnValue;
			} catch (final ExecutionException e) {
				firePostExecuteFailure(e);
				throw e;
			}
		}
		final NotHandledException e = new NotHandledException(
				"There is no handler to execute."); 
		fireNotHandled(e);
		throw e;
	}
	/**
	 * Notifies the listeners for this command that it has changed in some way.
	 * 
	 * @param commandEvent
	 *            The event to send to all of the listener; must not be
	 *            <code>null</code>.
	 */
	private final void fireCommandChanged(final CommandEvent commandEvent) {
		if (commandEvent == null) {
			throw new NullPointerException("Cannot fire a null event"); 
		}
		final Object[] listeners = getListeners();
		for (int i = 0; i < listeners.length; i++) {
			final ICommandListener listener = (ICommandListener) listeners[i];
			listener.commandChanged(commandEvent);
		}
	}
	/**
	 * Notifies the execution listeners for this command that an attempt to