Remove an unnecessary conditional
Test Board.occupiedPieces
Refactor the movegen test data

This will make way to add attack boards for each test datum.
It is easier to add the attack boards for the computable test
data than it is to create a completely new movegen engine to
test the current one.
Compute the attack for each test datum
Fix the attack board computations

The tests are all green again.
Merge pull request #89 from joichiro/testmovegen

Test the bitboard properties while testing movegen