Replaces previous mutable.Freeze logic with
commits that can live together with mutable data.
Finalize method is added if the implementation
needs to make sure that the immutable ref is
flushed to the driver. Refs are automaitcally
finalized when writable layers are created on
top of them.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Tonis Tiigi