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 String getConfigFileName( String reportDesignName )
	{
		if ( reportDesignName == null )
			return null;
		String[] result = reportDesignName.split( "\\." ); 
		String extensionName = result[result.length - 1];
		String configFileName = reportDesignName.substring( 0, reportDesignName
				.length( )
				- extensionName.length( ) )
				+ IBirtConstants.SUFFIX_DESIGN_CONFIG;
		return configFileName;
	}
	/**
	 * Get current format of parameter.
	 * 
	 * @param request
	 *            HttpServletRequest
	 * @param paramName
	 *            String
	 * 
	 * @return String
	 */
	public static String getFormat( HttpServletRequest request, String paramName )
	{
		if ( request == null || paramName == null )
			return null;
		return getParameter( request, paramName + "_format" ); 
	}
	/**
	 * @return the isWorkingFolderAccessOnly