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/CommandManager.java
}
	/**
	 * Removes an execution listener from this command manager.
	 * 
	 * @param listener
	 *            The listener to be removed; must not be <code>null</code>.
	 */
	public final void removeExecutionListener(final IExecutionListener listener) {
		if (listener == null) {
			throw new NullPointerException("Cannot remove a null listener"); 
		}
		if (executionListeners == null) {
			return;
		}
		executionListeners.remove(listener);
		if (executionListeners.isEmpty()) {
			executionListeners = null;
			
			final Iterator commandItr = handleObjectsById.values().iterator();
			while (commandItr.hasNext()) {
				final Command command = (Command) commandItr.next();
				command.removeExecutionListener(executionListener);
			}
			executionListener = null;
		}
	}
	/**
	 * Block updates all of the handlers for all of the commands. If the handler
	 * is <code>null</code> or the command id does not exist in the map, then
	 * the command becomes unhandled. Otherwise, the handler is set to the