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
/**
	 * Get report page from Http request. If frameset pattern, default page is
	 * 1.
	 * 
	 * @param request
	 *            http request
	 * @return report page number
	 */
	public static int getPage( HttpServletRequest request )
	{
		int page = getParameterAsInt( request, PARAM_PAGE );
		if ( page > 0 )
			return page;
		String servletPath = request.getServletPath( );
		if ( IBirtConstants.SERVLET_PATH_FRAMESET
				.equalsIgnoreCase( servletPath )
				&& PARAM_FORMAT_HTML.equalsIgnoreCase( getFormat( request ) ) )
		{
			page = 1;
		}
		else
		{
			page = 0;
		}
		return page;
	}
	/**
	 * Get report page range from Http request.
	 * 
	 * @param request