fstools: update to the latest version, makes interrupted first boot more reliable

Use xattr to store the filesystem initialization state of the overlay.
As long as the filesystem is not marked as initialized yet (happens in
/etc/init.d/done), all overlay data (except for sysupgrade.tgz) will be
discarded before the system is allowed to boot

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44942 3c298f89-4303-0410-b956-a3cf2f4a3e73