Bug 213671 Expose evaluate() method in IReportContext
Need Engine expose evaluate() method in IReportContext interface, this will be used to evaluate global Javascript expression in case there's no resultset bound to current report item.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/script/IReportContext.java
* @param locale
	 *            locale of message, if the input <code>locale</code> is
	 *            <code>null</code>, the locale for the current thread will
	 *            be used instead.
	 * @param params
	 *            string arguments used to format error messages
	 * @return the corresponding locale-dependent messages. Return
	 *         <code>null</code> if resoueceKey is blank.
	 */
	String getMessage( String key, Locale locale, Object[] params );
	
	/**
	 * Get the type of the current task.
	 * @return task type including:
	 * <li><b>0</b> for GetParameterDefinition Task</li>
	 * <li><b>1</b> for Run Task</li>
	 * <li><b>2</b> for Render Task</li>
	 * <li><b>3</b> for Run and Render Task</li>
	 * <li><b>4</b> for DataExtraction Task</li>
	 * <li><b>-1</b> default value for unknown task</li>
	 */
	int getTaskType();
	
	/**
	 * get the report design handle.
	 * @return report design handle
	 */
	ReportDesignHandle getDesignHandle( );
}