Fix StrokePolygon by copying the FillPolygon approach.
Since we didn't check the first point for overflow it could... well, overflow
sometimes, and that would result in a spurious line
Remove commented code
Introduce flags for blitting mask.
Remove palette from BlitMask as it's not needed.
Also print flags in Polygon::Print()
Fake transparency by skipping every other pixel when MASK_SHADE is set
Skip every other horizontal line instead, since it looks better.
Finally fixed BlitBitmapWithMask()
Style fix