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/utility/ParameterAccessor.java
*/
	public static Map pushAppContext( Map map, HttpServletRequest request )
	{
		if ( map == null )
			map = new HashMap( );
		
		String appContextKey = (String) request
				.getAttribute( ATTR_APPCONTEXT_KEY );
		
		if ( appContextKey != null )
			map.put( appContextKey, request
					.getAttribute( ATTR_APPCONTEXT_VALUE ) );
		return map;
	}
	/**
	 * Returns the encoding for export data.
	 * 
	 * @param request
	 * @return
	 */
	public static String getExportEncoding( HttpServletRequest request )
	{
		String encoding = getParameter( request, PARAM_EXPORT_ENCODING );
		
		if ( encoding == null )
			encoding = UTF_8_ENCODE;
		return encoding;
	}
	/**
	 * Check whether show the report title.