1. Previous triangulation is wrong - it missed the situation, the internal angle is large than 180.

HDU 3060 - Area2 (In triangulation).

1. Optimized the poly_clip_poly_area function. The precision is higher than before.
2. The triangulation at last failed, bacause the test data is not the simple polygon.
3. in triangle_judge, the triangle degenerates to a segment, in this situation, pass the judgement.
4. The ear-cutting method can solve all the situation except the polygon has internal cross.