Simple Frustum bug fix: "clone" and "constructor" should be real copies.

Unlike the constructors and clone methods of other math classes, the Frustum constructor and clone did not do proper copies of their parameters, leading to multiple Frustums referencing the same set of planes.

There was a bug in the Frustum clone unit test that allow for the bug in clone to get through the unit tests.  I've also expanded the constructor unit test to catch this type of issue in the future.