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 key
	 *            resource key of the user defined message.
	 * @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.
	 * @return the corresponding locale-dependent messages. Return
	 *         <code>null</code> if resoueceKey is blank.
	 */
	String getMessage( String key, Locale locale );
	/**
	 * Finds user-defined messages for the current thread's locale using parameters
	 * 
	 * @param key
	 *            resource key of the user-defined message.
	 * @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, Object[] params );
	/**
	 * Finds user-defined messages for the given locale using parameters
	 * <p>
	 * First we look up in the report itself, then look into the referenced
	 * message file. Each search uses a reduced form of Java locale-driven
	 * search algorithm: Language&Country, language, default.
	 * 
	 * @param key
	 *            resource key of the user defined message.