work aroung error message during boot if swapon is nt installed

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@12087 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/base-files/files/etc/init.d/fstab

@@ -55,7 +55,7 @@ start() {
 	config_foreach do_mount mount
 	config_foreach do_swapon swap
 	mount -a
-	swapon -a
+	[ -x /sbin/swapon ] && swapon -a
 }
 
 stop() {