t1304: fall back to $USER if $LOGNAME is not defined

For some reason $LOGNAME is not set anymore for me after an upgrade from
Ubuntu 11.04 to 11.10.  Use $USER in such a case.
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t1304-default-acl.sh

@@ -25,6 +25,11 @@ else
 	test_set_prereq SETFACL
 fi
 
+if test -z "$LOGNAME"
+then
+	LOGNAME=$USER
+fi
+
 check_perms_and_acl () {
 	test -r "$1" &&
 	getfacl "$1" > actual &&