Log write errors under SLT_Debug.

git-svn-id: http://www.varnish-cache.org/svn/trunk@3425 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_pool.c

@@ -126,6 +126,9 @@ WRK_Flush(struct worker *w)
 		i = writev(*w->wfd, w->iov, w->niov);
 		if (i != w->liov)
 			w->werr++;
+		WSL(w, SLT_Debug, *w->wfd,
+		    "Write error, len = %d/%d, errno = %s",
+		    i, w->liov, strerror(errno));
 	}
 	w->liov = 0;
 	w->niov = 0;