Bug 123972 [Undo] Support approval of undoable operation execution
In GMF we do some common validation on our commands before we proceed to execute, undo or redo them. This validation is external to the command's ability to execute, undo or redo itself. Registering an IOperationApprover with the operation history for this of validation would give us an elegant solution. However, the IOperationApprover only supports approval of undo and redo. We also require support for approval of operation execution. Would you consider adding a proceedExecuting() method to the IOperationApprover interface, or to an extension of the IOperationApprover interface?
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IOperationHistory.java
* will receive the <code>UNDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>, <code>INFO</code>,
	 * etc.) are not specifically interpreted by the history.  The operation will remain
	 * in the history and the returned status is simply passed back to the
	 * caller. For all severities other than <code>OK</code>, listeners
	 * will receive the <code>OPERATION_NOT_OK</code> notification
	 * instead of the <code>UNDONE</code> notification.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during undo.
	 */
	IStatus undo(IUndoContext context, IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;
	/**
	 * <p>
	 * Undo the specified operation
	 * </p>
	 * 
	 * @param operation
	 *            the operation to be undone
	 * @param monitor
	 *            the progress monitor to be used for the undo, or
	 *            <code>null</code> if no progress monitor is provided
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not