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
* 
	 * @param event
	 *            The execution event that will be used; never <code>null</code>.
	 */
	private final void firePreExecute(final ExecutionEvent event) {
		
		if (DEBUG_COMMAND_EXECUTION) {
			Tracing.printTrace("COMMANDS", "execute" + Tracing.SEPARATOR 
					+ "starting: id=" + getId() + "; event=" + event); 
		}
		if (executionListeners != null) {
			final Object[] listeners = executionListeners.getListeners();
			for (int i = 0; i < listeners.length; i++) {
				final IExecutionListener listener = (IExecutionListener) listeners[i];
				listener.preExecute(getId(), event);
			}
		}
	}
	/**
	 * Returns the category for this command.
	 * 
	 * @return The category for this command; never <code>null</code>.
	 * @throws NotDefinedException
	 *             If the handle is not currently defined.
	 */
	public final Category getCategory() throws NotDefinedException {
		if (!isDefined()) {
			throw new NotDefinedException(
					"Cannot get the category from an undefined command"); 
		}