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
String getOutputFormat( );
	/**
	 * get the render options used to render the 
	 * report.
	 * @return
	 */
	IRenderOption getRenderOption( );
	
	/**
	 * Get the application context
	 */
	Map getAppContext( );
	/**
	 * Get the http servlet request object
	 * 
	 */
	Object getHttpServletRequest( );
	/**
	 * Add the object to runtime scope. This object can only be retrieved in the
	 * same phase, i.e. it is not persisted between generation and presentation.
	 */
	void setGlobalVariable( String name, Object obj );
	/**
	 * Remove an object from runtime scope.
	 */
	void deleteGlobalVariable( String name );
	/**
	 * Retireve an object from runtime scope.
	 */
	Object getGlobalVariable( String name );