Bug 179743 Parameter Validate Event is not Called
I have tested the validate event on parameters and it never appears to get called.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineTask.java
* The parameter values that the caller has set explicitly
	 */
	protected HashMap inputValues = new HashMap( );
	/**
	 * The parameter values that will be used to run the report. It is a merged
	 * map between the input value and the default values.
	 */
	protected HashMap runValues = new HashMap( );
	/**
	 * Engine task type. for usage in BIRT scripting.
	 */
	protected int taskType = IEngineTask.TASK_UNKNOWN;
	/**
	 * @param engine
	 *            reference to report engine
	 * @param appContext
	 *            a user-defined object that capsulates the context for running
	 *            a task. The context object is passed to callback functions
	 *            (i.e., functions in image handlers, action handlers, etc. )
	 *            that are written by those who embeds engine in their
	 *            applications
	 */
	protected EngineTask( IReportEngine engine, IReportRunnable runnable )
	{
		taskID = id++;
		this.engine = engine;
		this.log = engine.getLogger( );
		
		executionContext = new ExecutionContext( this );