From http://redmine.lighttpd.net/projects/lighttpd/repository/revisions/2771
Subject: Silence annoying "connection closed: poll() -> ERR" error.log message (fixes #2257)
Upstream bug report: http://redmine.lighttpd.net/issues/2257

Index: trunk/src/connections.c
===================================================================
--- trunk.orig/src/connections.c	2010-11-08 18:06:48.000000000 +0100
+++ trunk/src/connections.c	2010-11-08 18:07:59.000000000 +0100
@@ -1224,7 +1224,8 @@
 
 			}
 		} else if (revents & FDEVENT_ERR) {
-#ifndef USE_LINUX_SIGIO
+			/* error, connection reset, whatever... we don't want to spam the logfile */
+#if 0
 			log_error_write(srv, __FILE__, __LINE__, "sd",
 					"connection closed: poll() -> ERR", con->fd);
 #endif