Work on fixing row/col permutations (to amend)
Solves the 16x16 grid. 20/01/2013. Restricted the values of the col and row freq tables to be more accurate (middle +- 2 rather than 1..size). Also added search annotations to the col and row freq tables to start at the most likely values (middle). Reordered the constraints, as it makes a difference to the number of backtracks etc.