If the chroot is exited with nonzero status, kiss-chroot runs `die
chroot failed`. Then, die runs `exit 1` which causes the trap to
execute. However, in this scope, "$@" is "chroot failed", so the trap
evaluates $1 to be "chroot" rather than the mountpoint given to the
kiss-chroot script. Then, the trap tries to unmount "chroot/dev" etc
rather than the true mountpoint.
This patch uses double quotes rather than single when setting the trap,
so that $1 is expanded then and the mountpoint is stored for when the
trap is called.