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
* successfully execute and that it was not added to the history. Any other
	 * severity code is not specifically interpreted by the history, and the
	 * operation will not be added to the history. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>DONE</code> notification.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during execution.
	 * 
	 */
	IStatus execute(IUndoableOperation operation, IProgressMonitor monitor,
			IAdaptable info) throws ExecutionException;
	/**
	 * <p>
	 * Return the limit on the undo and redo history for a particular context.
	 * </p>
	 * 
	 * @param context
	 *            the context whose limit is requested
	 * 
	 * @return the undo and redo history limit for the specified context.
	 */
	int getLimit(IUndoContext context);
	/**
	 * <p>
	 * Get the array of operations in the redo history for a the specified undo
	 * context. The operations are in the order that they were added to the
	 * history, with the most recently undone operation appearing last in the