harmonic: Incorrect scan line flood fill.

Flips exterior state by the number of times the Bresenham line
algorithm has drawn on a cell.

Fails at handling this Bresenham implementation’s line endpoints as the
end pixels are not drawn in the same quadrant direction as the line.
harmonic: Another incorrect scan line flood fill.

This version uses a lookahead to determine if a range of cells is
exterior or interior. It fails if a boundary cell range represents an
even number of edge crossings (only gets counted as one edge crossing).
This is only partially remedied by tracking the Bresenham edge
crossings.