Bug fixes. Added scryptn basecoin implementation.

It appears that hash_bin and block_hash_bin did different things in the original code. I added a distinct method for block_hash_bin to accommodate this. In the base, it simply returns hash_bin. I believe the return value of build_block was incorrect as the returned value would have gotten re-"join"ed in calc_algo. Also, the return value was never assigned to a variable for use in halfnode.py.