Fixed benchmark problems 10, 11, 48

[ytzi]

Summary of the changes:

• Problem 10 and 11: Fixed how the convex hull is computed -- now lower hull computations are correct and the endpoints for the lower hull is not included (since they are also endpoints for the upper hull). Should Fix Functionally Incorrect Baseline : Geometry - Convex_hull_perimeter & Convex_hull #37 but I have not tested it extensively.
• Problem 48: Should not clear the test vector after initialized it with a number of 0's.