Postpone digging into the future.

I.e.

Allow digging only for 1/X undug addresses:
Example for X=20
year 2016 allows to dig only addresses where sha256(ADDRESS)%20 == 16
year 2017 allows to dig only addresses where sha256(ADDRESS)%20 == 17
year 2018 allows to dig only addresses where sha256(ADDRESS)%20 == 18

So it takes 20 years to dig them all and then it can start new round.
In year 2037 everyone had the chance to claim all their Clams.

Value of X and exact address hashing algorithm is for future discussion. (May be is not necessary to hash it, as the address itself is just number)

txti