SweepEvents now generated correctly for planar triangles

~Fix: SweepEvents weren't generated for non-planar aabb-box areas if
 triangle was found to be planar.

~Change: FastKdTreeMemoryAllocator: Reinserted deletion code for iterators.
 (causes crash-> ?)
~Change: MathUtils now use <,<=,>,>= for floats.
~Fix: TriangleVerticeRefs now don't use hpvec2::length() anymore.
 This method just returned the dimension, not the vector length.
Merge branch 'fastkdtree-SS13-group1' of https://github.com/happah-graphics/happah into fastkdtree

Conflicts:
	happah/kdtree/FastKdTree.cpp