Bug 183919 [Enhancement] add a switch to determine whether to clean viewer image folder when session expires
in current viewer implementation, file in image folder is deleted when its corresponding session expires, could viewer add a switch to allow users to decide whether this deletion operation should be performed.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
return;
		
		__initParameters( request );
	}
	/**
	 * Prepare the report parameters
	 * 
	 * @param request
	 * @throws Exception
	 */
	protected void __initParameters( HttpServletRequest request )
			throws Exception
	{
		InputOptions options = new InputOptions( );
		options.setOption( InputOptions.OPT_REQUEST, request );
		options.setOption( InputOptions.OPT_LOCALE, locale );
		options.setOption( InputOptions.OPT_RTL, new Boolean( rtl ) );
		
		this.parameterDefList = getReportService( ).getParameterDefinitions(
				this.reportDesignHandle, options, false );
		
		if ( this.isDesigner
				&& !IBirtConstants.SERVLET_PATH_FRAMESET
						.equalsIgnoreCase( request.getServletPath( ) ) )
			parseConfigVars( request, parameterDefList );
		
		this.parametersAsString = getParsedParametersAsString(
				parameterDefList, request, options );
		
		if ( documentInUrl )