Comment 1 for bug 789803

Proposed solution:

Rationale: the static evaluation function should evaluate fast.

An "Unblocked piece" is a piece for which is valid either:
- Is on the first or last column (thus cannot be eaten)
- Has no opposing piece in front of it in the nearest three columns (if c is its column, these are c -1, c, c +1)

Each unblocked piece is given a weight proportional to how close it is to the king row.