BUGFIX-66

Bug 45: In Soviet Russia, Matrices Multiply YOU

This is Kronrod's algorithm for multiplying Boolean matrices (the Method of Four Russians).
It multiplies two 64x64 matrices (a times b) and adds the result to a third 64x64 matrix (c).
Each 64x64 matrix has 1-bit elements and is represented by an array of sixty-four 64-bit integers.
The matrices are row-major: Each row is one 64-bit integer. Column 0 is the least-significant bit.
1-bits in row r of matrix a select rows of matrix b. Selected rows are added to row r of matrix c.
Matrix b is split into 64/n sets of n rows. All subset sums are precomputed for each set of n rows.
The corresponding n bits from each row of matrix a are used to choose among these precomputed sums.
Addition is XOR in this implementation, but OR could be used instead.