[strategies][cartesian][cart_intersect] fix bug in Cartesian segment-segment
intersection strategy;
Bug: when exactly one segment degenerates to a point and is collinear with
the other segment, the strategy always sets the intersection count to 1;
Fix: check if the degenerate segment lies within the non-degenerate one
before setting the intersection count; if the point is outside the non-degenerate
segment declare the two segments as disjoint;
[test][distance] add some more P/L and L/L test cases; some of them
have triggered the bug in the Cartesian segment-segment intersection
strategy and the distance has produced wrong results; with the fix
in the Cartesian segment-segment intersection strategy, the distance
computation test cases added succeed;
Merge pull request #175 from mkaravel/fix/cartesian_segments_intersection

Fix/cartesian segments intersection